My best advice is to try and revert back to a version where the project was working. If that is not possible, you can try backing up and then removing the default map for the project, to see if you can get the editor to launch without this crash.
Given how blocking it is for our workflow, we won’t be able to wait for 4.13. Is there a Perforce CL number you could gave us so we can run the integration manually on our side?
Sorry about these troubles. We found several cases where Editor operations were breaking some assumptions in foliage (some of Undo/Redo operations, level SaveAs, level Duplicate). These should be fixed with CL# 3032336, 3057039 (scheduled for 4.13). Could you integrate these changes? These changes also remove asserts in foliage at loading time, so even if level was already saved with some broken foliage, Editor will still load that level without crashing. Broken foliage will lose a link to a component on which it was painted on (moving that component will not move foliage instances). These can be postfixed in Editor by Snapping foliage instances to ground (select instances + End key). If you can’t integrate those CLs I would recommend to replace all entries of:
UE_LOG(LogInstancedFoliage, Fatal
to
UE_LOG(LogInstancedFoliage, Error
in FoliageInstanceBase.cpp. That at least will allow to load crashing level in the Editor.
Instance base cache - integrity verification(3) is the exact same error i got when i dared to press simulate in the editor. now it doesnt open anymore, cant edit anything so basically one month of work is just gone because of this ----- engine! its awful to work with, unneccesary complicated and once you got the hang of it, it just crashes and ruins all of your work. thanks, really!