7
That room was deleted, since it contained less than 15 messages, see this FAQ. I used my chat superpowers to undelete it, although it is bizarre that this happens for rooms created from comments. I've added two messages, so that this won't happen again.
There seems to be a feature request to make this not happen, but apparently it is a sufficiently rare ...
3
I have just written a message to the Stack Exchange Team, and asked them to respond to this here. History has shown that this could take at least a few days.
3
As of last week, we also check for .net as a possible way to complete a valid domain, so https://stackexchange.com/leagues/week/mathoverflow will work going forward.
1
It seems that the new responsive design has fixed this issue:
Only top voted, non community-wiki answers of a minimum length are eligible
