Even after setting the folder as manga it doesn't work. Should I just email you a recording of the bug on 9.8.2 and the bug not appearing on 9.7.1?

I will try to replicate it, setting the folder as manga seems to be working just fine here, but you need to open the comics from YACReaderLibrary.

After you set the folder as manga, select a manga in that folder, open the "Edit" dialog using the pencil icon in the bottom bar and go to the "Publishing" tab, is "Manga" checked?. If not, close the dialog and use the "selected all" button, then the "set issue as manga" icon, both of them in the bottom bar too. After that, close all instances of YACReader, and reopen one of the mangas from YACReaderLibrary.