I was having this issue. What seemed to fix it for me was doing php flarum cache:clear
in terminal. Maybe there was a lot of old junk in my flarum’s trunk. Of course, I also removed a particular extension so that could have helped too.
Eventually, Flarum probably needs some cache settings and clearing options in core. More than the UnCache extension. I mean a button which does what php flarum cache:clear
does. Would that be possible?