@matthieuftmytb22 From Using Persistable Data in Verse | Unreal Editor for Fortnite Documentation | Epic Developer Community :
It seems like an intentional feature rather than a bug, I would like though some feature to reset weak_maps in case of a mess up.
However someone found this possible workaround as per this thread How To Remove weak_map From Project , I haven’t personally tested it myself but according to the thread creator they were able to revert to a published version from before the persistence data was added, and then the errors were not showing up, essentially letting them re-set and re-write a new weak_map, good luck.
Alternatively if you prefer to just recover the verse code you previously used that had the layout matching the one in the published version so the error can go you can follow the steps in this other thread Help pls problem with verse - #11 by Mineblo to find the different verse codes from different versions of your map and copy it back into your project