They should be in a folder called '.other-formats'. The folder is likely to be skipped by game engines, due to the '.' before its name. I did this specifically, so the duplicates in other formats wouldn't be loaded.
I see, thank you for a hint. I did not see that folder because folders and files having a leading dot in the name are hidden on macOS by default, and not everyone knows how to show them (press Cmd+Shift+. in Finder), so you should probably rename it in the next update.
