Hi @MagicThor,
You need to vote this up along with few others people
Taking a look at this IMHO its the “Cannot be used with Scene Graph Beta” that is the problem.
There is a lots of publishing error messages because “Scene Graph Beta” is experimentatal and you nned to check this.
There is a problem with 36.20 switching on “Scene Graph Beta” by default therefore Publishing validation will stop anything referencing “Experimental/Beta”. The “Extra” content is probably seen as Experimental. Could you try breaking/deleting the reference in content browser, which have done before to allow validation.
All materials must be imported as props
Perhaps you cannot do this on refence content.
Here is documentation
Importing Assets in Unreal Editor for Fortnite | Fortnite Documentation | Epic Developer Community
Try turning off “Scene Graph Beta” in myproject.uefnproject
This could be just another bug inUEFN 36.20