I was perhaps giving the bug a little too much credit there. This one was more the responsibility of @Naz but to be honest with you he fixed it last week and I don't think any of us realised. Or at least I didn't
It says cache rebuilding has been successful but nothing has changed..
Since my usage of icons might be weird, I just put a <xf:fa>-tag with icon on a random template (forum_view) to see if it would work/load and I rebuilt the cache for icon usage again but nothing is changing (fwiw, I'm on a localhost machine rn - could that be a factor?)