Ugh, that sucks. I'm sorry you have to deal with that. I had a similar experience on another site, though I think I only had like 20 episodes max (I stopped posting there for unrelated reasons). You know it's them and not you, but boy can it be frustrating...
Long tangent about my experience:
In my case, the guy would post criticisms in a derogatory tone every time I updated. I had my suspicions which were later proven right: it was one guy using multiple accounts to 1) insult other creators, and 2) flip out at people who posted criticisms (including very polite, constructive ones) on HIS own comic.
In fact, some of the criticisms he left on my comic were re-worded versions of the criticisms people posted on his own comic. Which was funny because the issues described in those critiques were clearly not present in my comic. In retrospect, he was probably struggling, emotionally. He probably posted those comments because he wanted to say, "people said shit like this about my own comic, and I feel really upset about it. Am I the only one who feels that way when that happens?" But he couldn't talk about it like a normal person due to some kinda emotional hang-up. Or so I'm guessing.
On his main account, the one he was using to upload his comic, he was overly friendly to me and would even talk about possibly visiting me in person. ¯_(ツ)_/¯