It sucks being a tenant and having to pick our battles.

I'm guessing ray white or Barry plant - I've had terrible terrible experiences with them both. My current one is pretty good though, no major issues with them yet -knock on wood-

See if you can find a fungicide maybe, and keep the cats out of that room if you apply it. My Epping house had the same issue with mushrooms in the bathroom, because the landlord refused to fix the leaky toilet in there. Had to use the dingy one in the laundry lol. He was a slumlord though, so I didn't bother trying to fix it myself.