all messages read but 2 unread ones appear all the time

[panoramia]

Dear Sirs,

I've got a problem with vBulletin 5.1.7. There is a user that cannot get read of "2 unread messages", however all messages and notifications are read, I've triple checked it and there is nothing to be unread.

There is no way to get rid of these 2 unread messages for this user. ALL messages are read. I went one by one over all sections on the Message Center, nothing there. I even marked all channels as read just in case. It didn't fix anything, still there.

You can see the issue in the attachment:

What can be the problem and how can I fix this?

Thanks in advance.
Regards,
Alfonso

[Dominic]

Have you tried to clear the system cache in the Admin-CP -> Maintenance?