Hi all:
We believe that we’ve identified the root cause of this issue and this bug will be fixed in an upcoming UEFN release. In the meantime, thanks to everyone here who contributed information regarding this issue. Please see an official note regarding the known workaround here: Fortnite Ecosystem v29.00 with Known Issues - #7 by Flak
(You should only need to delete the VerseSnapshot folder for your project that you are having issues with, not the entire VerseProject folder)