.umap file was corrupted
In case it happens to you, here’s how to fix it:
WARNING: you have to have revision ON before the pb happens
remove .umap from content (+make a full copy of the the project just in case)
open the project, should work fine
open revision and select the version before the latest, sync
if uefn stays open, means you’re on the right way
go get the .umap from that version in the file and copy/paste it elsewhere
go back to your project on uefn, load the last revision, uefn crashes, no worries
copy/paste the .umap you just collected to replace the one in the project file folder Content
except for the map modifications you made between the 2revision versions all the rest should be fine.
Have a nice day