For me the red line “Last Visit” is working correct inside a thread but in the view of threads it is much further back in the past than my actual last visit.
In the early days of the new forum it was working correct for me. I think it startet at the time when the left side menu was introduced.
Can think of issues like reading when not signed (eliciting the continuous "you seem to like… don’t you want to create an account?) and erased cookies to throw a curve ball.
(I’ve found a scary amount of tracking on this forum system, just dig into your account details, so cookies are ditched daily through a little browser extension)
My guess would be that it’s related with the import of the old forum content. That is if we’re talking about community categories. Dunno if this occurs for other ones.