For IK to work on custom characters you need to add these two nodes to the post process anim BP
( copy this text (exactly) to the clipboard then paste it into the BP ) - the author should do this too so everyone gets the fix
Begin Object Class=/Script/AnimGraph.AnimGraphNode_CopyBone Name="AnimGraphNode_CopyBone_2"
Node=(SourceBone=(BoneName="foot_l"),TargetBone=(BoneName="ik_foot_l"),ControlSpace=BCS_WorldSpace)
ShowPinForProperties(0)=(PropertyName="SourceBone",PropertyFriendlyName="Source Bone",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_CopyBone:SourceBone", "Source Bone Name to get transform from"),CategoryName="Copy")
ShowPinForProperties(1)=(PropertyName="TargetBone",PropertyFriendlyName="Target Bone",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_CopyBone:TargetBone", "Name of bone to control. This is the main bone chain to modify from. *"),CategoryName="Copy")
ShowPinForProperties(2)=(PropertyName="bCopyTranslation",PropertyFriendlyName="Copy Translation",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_CopyBone:bCopyTranslation", "If Translation should be copied"),CategoryName="Copy",bShowPin=True,bCanToggleVisibility=True)
ShowPinForProperties(3)=(PropertyName="bCopyRotation",PropertyFriendlyName="Copy Rotation",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_CopyBone:bCopyRotation", "If Rotation should be copied"),CategoryName="Copy",bShowPin=True,bCanToggleVisibility=True)
ShowPinForProperties(4)=(PropertyName="bCopyScale",PropertyFriendlyName="Copy Scale",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_CopyBone:bCopyScale", "If Scale should be copied"),CategoryName="Copy",bShowPin=True,bCanToggleVisibility=True)
ShowPinForProperties(5)=(PropertyName="ControlSpace",PropertyFriendlyName="Control Space",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_CopyBone:ControlSpace", "Space to convert transforms into prior to copying components"),CategoryName="Copy")
ShowPinForProperties(6)=(PropertyName="ComponentPose",PropertyFriendlyName="Component Pose",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_SkeletalControlBase:ComponentPose", "Input link"),CategoryName="Links",bShowPin=True)
ShowPinForProperties(7)=(PropertyName="Alpha",PropertyFriendlyName="Alpha",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_SkeletalControlBase:Alpha", "Current strength of the skeletal control"),CategoryName="Settings",bShowPin=True,bCanToggleVisibility=True)
ShowPinForProperties(8)=(PropertyName="AlphaScaleBias",PropertyFriendlyName="Alpha Scale Bias",PropertyTooltip="Alpha Scale Bias",CategoryName="Settings")
ShowPinForProperties(9)=(PropertyName="LODThreshold",PropertyFriendlyName="LOD Threshold",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_SkeletalControlBase:LODThreshold", "* Max LOD that this node is allowed to run
* For example if you have LODThreadhold to be 2, it will run until LOD 2 (based on 0 index)
* when the component LOD becomes 3, it will stop update/evaluate
* currently transition would be issue and that has to be re-visited"),CategoryName="Performance")
NodePosX=-1216
NodePosY=-64
NodeGuid=3D529F464631BCBC2571CB90F6F2AD35
CustomProperties Pin (PinId=43D7FC874A52A88DCDB27693B5000DB7,PinName="bCopyTranslation",PinFriendlyName="Copy Translation",PinToolTip="Copy Translation
Boolean
If Translation should be copied",PinType.PinCategory="bool",PinType.PinSubCategory="",PinType.PinSubCategoryObject=None,PinType.PinSubCategoryMemberReference=(),PinType.PinValueType=(),PinType.ContainerType=None,PinType.bIsArray=False,PinType.bIsReference=False,PinType.bIsConst=False,PinType.bIsWeakPointer=False,DefaultValue="true",AutogeneratedDefaultValue="False",PersistentGuid=00000000000000000000000000000000,bHidden=False,bNotConnectable=False,bDefaultValueIsReadOnly=False,bDefaultValueIsIgnored=False,bAdvancedView=False,bOrphanedPin=False,)
CustomProperties Pin (PinId=675B2AAC4EB23090EC92EFB6F0ED8FA3,PinName="bCopyRotation",PinFriendlyName="Copy Rotation",PinToolTip="Copy Rotation
Boolean
If Rotation should be copied",PinType.PinCategory="bool",PinType.PinSubCategory="",PinType.PinSubCategoryObject=None,PinType.PinSubCategoryMemberReference=(),PinType.PinValueType=(),PinType.ContainerType=None,PinType.bIsArray=False,PinType.bIsReference=False,PinType.bIsConst=False,PinType.bIsWeakPointer=False,DefaultValue="true",AutogeneratedDefaultValue="False",PersistentGuid=00000000000000000000000000000000,bHidden=False,bNotConnectable=False,bDefaultValueIsReadOnly=False,bDefaultValueIsIgnored=False,bAdvancedView=False,bOrphanedPin=False,)
CustomProperties Pin (PinId=921880B64C270A813E9EFEB4E0B0B65D,PinName="bCopyScale",PinFriendlyName="Copy Scale",PinToolTip="Copy Scale
Boolean
If Scale should be copied",PinType.PinCategory="bool",PinType.PinSubCategory="",PinType.PinSubCategoryObject=None,PinType.PinSubCategoryMemberReference=(),PinType.PinValueType=(),PinType.ContainerType=None,PinType.bIsArray=False,PinType.bIsReference=False,PinType.bIsConst=False,PinType.bIsWeakPointer=False,DefaultValue="False",AutogeneratedDefaultValue="False",PersistentGuid=00000000000000000000000000000000,bHidden=False,bNotConnectable=False,bDefaultValueIsReadOnly=False,bDefaultValueIsIgnored=False,bAdvancedView=False,bOrphanedPin=False,)
CustomProperties Pin (PinId=1064BFA340A02FC1050B8A89301484EA,PinName="ComponentPose",PinFriendlyName="Component Pose",PinToolTip="Component Pose
Component Space Pose Link Structure
Input link",PinType.PinCategory="struct",PinType.PinSubCategory="",PinType.PinSubCategoryObject=ScriptStruct'"/Script/Engine.ComponentSpacePoseLink"',PinType.PinSubCategoryMemberReference=(),PinType.PinValueType=(),PinType.ContainerType=None,PinType.bIsArray=False,PinType.bIsReference=False,PinType.bIsConst=False,PinType.bIsWeakPointer=False,DefaultValue="(LinkID=-1,SourceLinkID=-1)",AutogeneratedDefaultValue="(LinkID=-1,SourceLinkID=-1)",LinkedTo=(AnimGraphNode_LocalToComponentSpace_0 79D2C07643B31E75C8555BA9137569CD,),PersistentGuid=00000000000000000000000000000000,bHidden=False,bNotConnectable=False,bDefaultValueIsReadOnly=False,bDefaultValueIsIgnored=False,bAdvancedView=False,bOrphanedPin=False,)
CustomProperties Pin (PinId=AF2B6F824D6ED80EA2BBE29F16B4AF4D,PinName="Alpha",PinFriendlyName="Alpha",PinToolTip="Alpha
Float
Current strength of the skeletal control",PinType.PinCategory="float",PinType.PinSubCategory="",PinType.PinSubCategoryObject=None,PinType.PinSubCategoryMemberReference=(),PinType.PinValueType=(),PinType.ContainerType=None,PinType.bIsArray=False,PinType.bIsReference=False,PinType.bIsConst=False,PinType.bIsWeakPointer=False,DefaultValue="1.000000",AutogeneratedDefaultValue="1.000000",PersistentGuid=00000000000000000000000000000000,bHidden=False,bNotConnectable=False,bDefaultValueIsReadOnly=False,bDefaultValueIsIgnored=False,bAdvancedView=False,bOrphanedPin=False,)
CustomProperties Pin (PinId=072ECDD041D5929851356895BC6DA776,PinName="Pose",Direction="EGPD_Output",PinType.PinCategory="struct",PinType.PinSubCategory="",PinType.PinSubCategoryObject=ScriptStruct'"/Script/Engine.ComponentSpacePoseLink"',PinType.PinSubCategoryMemberReference=(),PinType.PinValueType=(),PinType.ContainerType=None,PinType.bIsArray=False,PinType.bIsReference=False,PinType.bIsConst=False,PinType.bIsWeakPointer=False,LinkedTo=(AnimGraphNode_CopyBone_0 1064BFA340A02FC1050B8A89301484EA,),PersistentGuid=00000000000000000000000000000000,bHidden=False,bNotConnectable=False,bDefaultValueIsReadOnly=False,bDefaultValueIsIgnored=False,bAdvancedView=False,bOrphanedPin=False,)
End Object
Begin Object Class=/Script/AnimGraph.AnimGraphNode_CopyBone Name="AnimGraphNode_CopyBone_0"
Node=(SourceBone=(BoneName="foot_r"),TargetBone=(BoneName="ik_foot_r"),ControlSpace=BCS_WorldSpace)
ShowPinForProperties(0)=(PropertyName="SourceBone",PropertyFriendlyName="Source Bone",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_CopyBone:SourceBone", "Source Bone Name to get transform from"),CategoryName="Copy")
ShowPinForProperties(1)=(PropertyName="TargetBone",PropertyFriendlyName="Target Bone",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_CopyBone:TargetBone", "Name of bone to control. This is the main bone chain to modify from. *"),CategoryName="Copy")
ShowPinForProperties(2)=(PropertyName="bCopyTranslation",PropertyFriendlyName="Copy Translation",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_CopyBone:bCopyTranslation", "If Translation should be copied"),CategoryName="Copy",bShowPin=True,bCanToggleVisibility=True)
ShowPinForProperties(3)=(PropertyName="bCopyRotation",PropertyFriendlyName="Copy Rotation",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_CopyBone:bCopyRotation", "If Rotation should be copied"),CategoryName="Copy",bShowPin=True,bCanToggleVisibility=True)
ShowPinForProperties(4)=(PropertyName="bCopyScale",PropertyFriendlyName="Copy Scale",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_CopyBone:bCopyScale", "If Scale should be copied"),CategoryName="Copy",bShowPin=True,bCanToggleVisibility=True)
ShowPinForProperties(5)=(PropertyName="ControlSpace",PropertyFriendlyName="Control Space",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_CopyBone:ControlSpace", "Space to convert transforms into prior to copying components"),CategoryName="Copy")
ShowPinForProperties(6)=(PropertyName="ComponentPose",PropertyFriendlyName="Component Pose",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_SkeletalControlBase:ComponentPose", "Input link"),CategoryName="Links",bShowPin=True)
ShowPinForProperties(7)=(PropertyName="Alpha",PropertyFriendlyName="Alpha",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_SkeletalControlBase:Alpha", "Current strength of the skeletal control"),CategoryName="Settings",bShowPin=True,bCanToggleVisibility=True)
ShowPinForProperties(8)=(PropertyName="AlphaScaleBias",PropertyFriendlyName="Alpha Scale Bias",PropertyTooltip="Alpha Scale Bias",CategoryName="Settings")
ShowPinForProperties(9)=(PropertyName="LODThreshold",PropertyFriendlyName="LOD Threshold",PropertyTooltip=NSLOCTEXT("UObjectToolTips", "AnimNode_SkeletalControlBase:LODThreshold", "* Max LOD that this node is allowed to run
* For example if you have LODThreadhold to be 2, it will run until LOD 2 (based on 0 index)
* when the component LOD becomes 3, it will stop update/evaluate
* currently transition would be issue and that has to be re-visited"),CategoryName="Performance")
NodePosX=-1216
NodePosY=160
ErrorType=4
NodeGuid=BED04FC94B0BAF58A561A9950F18827C
CustomProperties Pin (PinId=43D7FC874A52A88DCDB27693B5000DB7,PinName="bCopyTranslation",PinFriendlyName="Copy Translation",PinToolTip="Copy Translation
Boolean
If Translation should be copied",PinType.PinCategory="bool",PinType.PinSubCategory="",PinType.PinSubCategoryObject=None,PinType.PinSubCategoryMemberReference=(),PinType.PinValueType=(),PinType.ContainerType=None,PinType.bIsArray=False,PinType.bIsReference=False,PinType.bIsConst=False,PinType.bIsWeakPointer=False,DefaultValue="true",AutogeneratedDefaultValue="False",PersistentGuid=00000000000000000000000000000000,bHidden=False,bNotConnectable=False,bDefaultValueIsReadOnly=False,bDefaultValueIsIgnored=False,bAdvancedView=False,bOrphanedPin=False,)
CustomProperties Pin (PinId=675B2AAC4EB23090EC92EFB6F0ED8FA3,PinName="bCopyRotation",PinFriendlyName="Copy Rotation",PinToolTip="Copy Rotation
Boolean
If Rotation should be copied",PinType.PinCategory="bool",PinType.PinSubCategory="",PinType.PinSubCategoryObject=None,PinType.PinSubCategoryMemberReference=(),PinType.PinValueType=(),PinType.ContainerType=None,PinType.bIsArray=False,PinType.bIsReference=False,PinType.bIsConst=False,PinType.bIsWeakPointer=False,DefaultValue="true",AutogeneratedDefaultValue="False",PersistentGuid=00000000000000000000000000000000,bHidden=False,bNotConnectable=False,bDefaultValueIsReadOnly=False,bDefaultValueIsIgnored=False,bAdvancedView=False,bOrphanedPin=False,)
CustomProperties Pin (PinId=921880B64C270A813E9EFEB4E0B0B65D,PinName="bCopyScale",PinFriendlyName="Copy Scale",PinToolTip="Copy Scale
Boolean
If Scale should be copied",PinType.PinCategory="bool",PinType.PinSubCategory="",PinType.PinSubCategoryObject=None,PinType.PinSubCategoryMemberReference=(),PinType.PinValueType=(),PinType.ContainerType=None,PinType.bIsArray=False,PinType.bIsReference=False,PinType.bIsConst=False,PinType.bIsWeakPointer=False,DefaultValue="False",AutogeneratedDefaultValue="False",PersistentGuid=00000000000000000000000000000000,bHidden=False,bNotConnectable=False,bDefaultValueIsReadOnly=False,bDefaultValueIsIgnored=False,bAdvancedView=False,bOrphanedPin=False,)
CustomProperties Pin (PinId=1064BFA340A02FC1050B8A89301484EA,PinName="ComponentPose",PinFriendlyName="Component Pose",PinToolTip="Component Pose
Component Space Pose Link Structure
Input link",PinType.PinCategory="struct",PinType.PinSubCategory="",PinType.PinSubCategoryObject=ScriptStruct'"/Script/Engine.ComponentSpacePoseLink"',PinType.PinSubCategoryMemberReference=(),PinType.PinValueType=(),PinType.ContainerType=None,PinType.bIsArray=False,PinType.bIsReference=False,PinType.bIsConst=False,PinType.bIsWeakPointer=False,DefaultValue="(LinkID=-1,SourceLinkID=-1)",AutogeneratedDefaultValue="(LinkID=-1,SourceLinkID=-1)",LinkedTo=(AnimGraphNode_CopyBone_2 072ECDD041D5929851356895BC6DA776,),PersistentGuid=00000000000000000000000000000000,bHidden=False,bNotConnectable=False,bDefaultValueIsReadOnly=False,bDefaultValueIsIgnored=False,bAdvancedView=False,bOrphanedPin=False,)
CustomProperties Pin (PinId=AF2B6F824D6ED80EA2BBE29F16B4AF4D,PinName="Alpha",PinFriendlyName="Alpha",PinToolTip="Alpha
Float
Current strength of the skeletal control",PinType.PinCategory="float",PinType.PinSubCategory="",PinType.PinSubCategoryObject=None,PinType.PinSubCategoryMemberReference=(),PinType.PinValueType=(),PinType.ContainerType=None,PinType.bIsArray=False,PinType.bIsReference=False,PinType.bIsConst=False,PinType.bIsWeakPointer=False,DefaultValue="1.000000",AutogeneratedDefaultValue="1.000000",PersistentGuid=00000000000000000000000000000000,bHidden=False,bNotConnectable=False,bDefaultValueIsReadOnly=False,bDefaultValueIsIgnored=False,bAdvancedView=False,bOrphanedPin=False,)
CustomProperties Pin (PinId=072ECDD041D5929851356895BC6DA776,PinName="Pose",Direction="EGPD_Output",PinType.PinCategory="struct",PinType.PinSubCategory="",PinType.PinSubCategoryObject=ScriptStruct'"/Script/Engine.ComponentSpacePoseLink"',PinType.PinSubCategoryMemberReference=(),PinType.PinValueType=(),PinType.ContainerType=None,PinType.bIsArray=False,PinType.bIsReference=False,PinType.bIsConst=False,PinType.bIsWeakPointer=False,LinkedTo=(AnimGraphNode_ModifyBone_102 4324171144775F12BF4610A840698087,),PersistentGuid=00000000000000000000000000000000,bHidden=False,bNotConnectable=False,bDefaultValueIsReadOnly=False,bDefaultValueIsIgnored=False,bAdvancedView=False,bOrphanedPin=False,)
End Object