Site is telling me I have 1 unread message, but when I click on it, the flag disappears and it says I have no unread messages. Navigating to, or refreshing a, page, brings the flag back. I’m talking about the message flag at top right y my avatar.
There was a spammy user active earlier. If you have your 'Allow private messages from' setting set to 'everyone', then this may be related.
That could be it and presumably the message has been deleted which explains why I can't see it. However, the flag still persists.