Board Game Arena

On Monday, when going to the mySQl console (https://studio.boardgamearena.com/db/index.php) , I could see my tutorial game (Reversi) database and tables. However, since yesterday, they have "disappeared". I can only see the "information_schema" now.

Any idea what caused this?

If the games were finished it's completely normal. Those databases are deleted every once in a while. There was also a database server maintenance on Tuesday. But your DBs should have been migrated onto the new server.

Just like in prod, after a while without games played, tables are closed automatically and databases are garbage collected to free space.
Probably your table was realtime; my advice would be to create turn based tables if you want to keep a table open long term (there is still a limit, but it's over a month).

Edit: just noticed that another answer was posted at the same time, and I wanted to clarify that database maintenance on Tuesday was only for the main site, not the studio. There was no maintenance on the studio.

Thank you both. That was exactly the issue.

PS: I created a turn-based table, so that I have more time to study the database.