Board Game Arena

What exactly is happening right now? The server was briefly online for a couple of hours, and is it the same today? Is there any explanation?

Same...

The devs are giving updates in the other thread:

https://boardgamearena.com/forum/viewtopic.php?t=38047

They are temporarily unlocking the game at times while they try to fix the server problems from the latest update. That update will allow players to choose which decks (Artifex, Bubulcus etc) they use for the game.

It’s not fixed yet but they are working on it.