For some reason, ItemExchange detects unaccepted file formats in my set, even though it only consists of .gbx files and folders containing .gbx files. Am I doing something wrong? Other sets with the same file structure upload fine.

Edit: I moved all the files to a new folder system I re-created. It still won't work.

Edit #2: I moved all the subfolders to a new master folder structure in a new location and archived that, which uploaded without issue. Issue solved, but this is a strange error.