UEFN giving me an "Illegal Reference" error when I try to upload a private version of my migrated map

I made a map that I want to migrate to another one and use it as a template for multiple other maps for different genres, but when I migrate everything to the new map and try to launch a session or upload a private version it gives me an “Illegal Reference” error for pretty much all of the signs from the Fortnite library as well as any objects I’ve modified or are custom. Also, running Fix-up literally does nothing, it says it’s all fixed but when i run it again it gives me the same error for all the same items. I really don’t want to have to replace all of the signs and objects because there are hundreds, I’m just wondering if anyone has any knowledge for a workaround for this error or what I have to do to fix the issue, thank you.