Page is finally back ! Thank you very much for your answers.
Really wish there was a way to prevent this, I guess I'll just have to pray that each new update goes fine now (or just not update recently released games at all).
While the automated checks are secret like hechelion said, please make sure you follow the quality guidelines, in particular point 1: avoid publishing your page before it's ready. I suspect a lot of people get impatient, and it could be a reason why this keeps happening.
Maybe it was unclear, but the game was initially made for a game jam, so.......... It gets published when the deadline of the jam is reached (doesn't really have anything to do with impatience in my case).
I also recently got an answer to my ticket from the support, and apparently it could have been caused by the fact I had an other page of the same game with restricted access for private testing purposes ? I am not totally sure, tho. Either way, the sanction from the algorithm was a bit disproportionate compared to the reason it got flagged in the first place. If I can suggest an idea, having different degrees of flagging before putting a page in quarantine could be a better solution ?