Sudden red "topic not available" message
I was typing a reply to a post, when suddenly the following red message appeared (before taking the screenshot, I erased the relatively short text I had already typed there):

After reloading, the thread had a post from other user, which was not there previously. However, I've encountered previously that threads I was commenting on had seen comments from other users meantime. Also, the text of that message nor its appearance (red = something went very wrong) does not reflect this event.
JW
