TeamF I have tried disabling all extensions except for mentions, tried syncing your forum, checking server-side and browser logs, without any luck.
The only error that could be useful is this one from browser console:
It is related to the service worker of the PWA extension. So I tried to disable that extension, sync your forum and clear my browser cache (even tried another browser that never visited your forum, so that the service worker file wouldn't be cached). I have updated all extensions of your forum with a hope that this might be fixed somewhere, but that didn't help either. I'm sorry, but I have no idea what it could be at this point (maybe it's related to Flarum core?). Perhaps someone else at this forum might know more...
A small announcement for everyone - I have reset SMTP settings for all forums to ensure that E-mail is being sent properly. Please, see my latest announcement above for context.