I seen this issue pop up in posts many months back. Don’t remember a solution or reason though.
Have you got the prefabs still attached to the prefab root or put into seperate folders ?
Have you got OneDrive backup on your projects folder ?, it conflicts with UEFN, but usually just “undeletes” odd things here and there.
Could imagine it restoring stuff to an earlier transform location, if it thinks it needs restoring because it doesn’t communicate changes with UEFN too well ???..
did you put the prefabs in this location when you first placed them down ?
What cell size and loading range are you using ?