I am just learning Unreal. I am doing 1d blend animation between walk and run. character has weapon in her hand but while doing blend animation at some point sword weapon leaves it position bu at the start and end it keeps it position. Please check the attached video for proper visualization. Both animation done with same rig and with same properties.
If the sword is not a child object in the original rig and part of the hierarchy and only atatched in maya via constraints then you will face these problems. I suggest do the following:
1 - make sword always be part of the rig in the hierarchy with proper parenting, only if your character wont change weapons later in game and the sword will always be part of the character.
2- import sword separately in UE and attach it there to a socket on a bone. this setup most flexibly for weapon changes.