Thanks JenS et al for informing us about this problem. Tbh you could have informed us about it earlier, since it's been bugging us all day.
But it is good to know that this problem is not with ADZbuzz, although I was kinda hoping that this was caused by a sudden increase of traffic to ADZbuzz

The forum has been up all day, here is the latest update of our senior developer who is montoring the situation:
https://forum.adzbuzz.com/forum/main-forum/adzbuzz-bug-fixes/6106-error-502?p=6130#post6130 As mentioned in his reply, we have invested and are already working on a superior system to have 100% uptime at all times. More info about that will be posted in the next update after the new dev meeting this Tuesday.
Thanks JensS for you answer. Friday seemed to be an all around bad day, in addition to ADZbuzz I had trouble getting to the forums and I also had trouble getting here (got "site is busy ..." on severall occasions). But it's all good now.