[2018.04.05-12.42.10:669][ 0]LogProperty: Warning: Serialized Class /Script/CoreUObject.LinkerPlaceholderExportObject for a property of Class /Script/UMG.CanvasPanel. Reference will be nullptred.
Property = ObjectProperty /Game/Blueprints/UI/ProgressBarWidget.ProgressBarWidget_C:CanvasPanel_0
Item = LinkerPlaceholderExportObject /Game/Blueprints/UI/ProgressBarWidget.PLACEHOLDER-INST_of_ProgressBarWidget_C_0:PLACEHOLDER-INST_of_WidgetTree_1.PLACEHOLDER-INST_of_CanvasPanel_2
[2018.04.05-12.42.10:669][ 0]LogProperty: Warning: Serialized Class /Script/CoreUObject.LinkerPlaceholderExportObject for a property of Class /Script/UMG.ProgressBar. Reference will be nullptred.
Property = ObjectProperty /Game/Blueprints/UI/ProgressBarWidget.ProgressBarWidget_C:GenericProgressBar
Item = LinkerPlaceholderExportObject /Game/Blueprints/UI/ProgressBarWidget.PLACEHOLDER-INST_of_ProgressBarWidget_C_0:PLACEHOLDER-INST_of_WidgetTree_1.PLACEHOLDER-INST_of_ProgressBar_4
Looks like it could be an issue with one of your Widgets. I would suggest making backups of your Widget blueprints, removing them from the project temporarily, and attempting to open the project. It also seems that these logs are from before downloading the Editor Symbols for Debugging, as it still lists the functions in the callstack as “UnknownFunction”. Please provide the log from attempting to open the project after having the symbols installed.