It's a known issue with the GOG Subforums, as long as they don't have a thread in them, it'll show the last activity as "Nov 30, -0001". As soon as a thread is created, this is resolved. You can check the No Man's Sky subforum, for instance. That game hasn't been released yet, but the last activity date is not bugged because the forum is not empty.
Sorry for yet another necro! I stumbled again on this issue but this time, it's caused by different reasons.
As you can see on the first attachment, it says "Nov. 30, -0001" for the Kingdom Rush
hub, even though you can see on the second attachment that it definitely has some threads in it. Is it because a new game in the series (Kingdom Rush: Frontiers
) just released today, and for this reason, the counters have been reset? Edit.
Attachments added. I should have put them before typing my post.. :P