ID:2102026
 
Far as I knew, it was up there yesterday, and the server is still online (with 86 players) but noone can find it on the Hub.

Is this some silly 510 thing since we are 509 while we convert our code?

It's a SS13 Server, specifically, Colonial Marines.
The server may have stopped reporting to the hub properly after yesterday's maintenance. I believe you'll find that changing the hosting mode from public to private and back again will likely fix it.