I have this problem too. It happens when cooking a converted project from 4.20 to 4.21 and it’s apparently about a widget. Whenever I remove the offending widget, a new error shows up with another.
The strangest part of my output is
LogUObjectHash: Warning: Ambiguous search, could be StructProperty /Script/Engine.KismetSystemLibrary:BoxTraceMulti.End or Function /Game/BP/UI/Messages/UIQMSGItem.SKEL_UIQMSGItem_C:End
I don’t have this asset, and it’s not a SKEL_ but a widget. and I don’t have any idea how to fix it at the moment