DavecUK I am wondering if there is a rogue extension causing it?
I have made the forum quite feature rich.
I can’t say where the issue is coming from, but I have now learned how to use the forum so it doesn’t bother me anymore. As @dndrich mentioned, if pressing a link in an email notification, or opening a new tab, or sometimes without doing anything naughty - the standard features (reply to, quote, like, uploading photos etc.) would not be there, or the “ooops” message would appear. But now I know not to mess about - all I need to do to sort things out is close the tab where the forum is opened and open it again - and the issues are gone (for me, at least).
The problem, I think, is for new people. Until you figure out how it works here, know you can’t open a message in a new tab, and understand that whenever you see a problem you just leave the forum and come back - you might struggle and think the forum is broken. Not a problem once you know, but can be off putting until then.