Here we go again 😭

I swear, I am a begonia serial killer. What the hell is wrong with it 😭 it was doing really good in my new greenhouse cabinet, but now it’s not very happy. It’s getting droopy, yellowing, and crisping leaves. The new leaves are coming in really nice, but all the other leaves are dying. I hadn’t watered it for a while and then it drooped a bit, watered it, it perked back up, and now it’s dying. The roots don’t seem like they’re rotting. They look fine. Could this be a fungal issue??