Most likely somebody doesn’t like you & spent a lot of time reporting many of your posts. Those posts have been deleted by a moderator.
Yep, that's the likely reason. I just had one of my posts deleted, though I have no idea which one it was since I didn't get a PM from a mod. I'm assuming it was probably an entire thread I posted in that got nuked.
OP, I get the point of this thread--that's a lot of posts you got deleted all at once. But if a mod decides you were consecuposting or that a thread you posted in deserves to be trashcanned, this is going to happen from time to time. I have signatures blocked so I don't know if you're in a campaign, but if these posts were old then it shouldn't affect you if the campaign manager is counting posts made during a specific time frame. In any case, there isn't much you can do about it.
does it depend on the discretion of the mod of that subforum?
I'd assume that is the case.
Definitely the case in my experience. Some moderators are way more aggressive in deleting posts and tend to rely on the judgement of the reporters, who could be mistaken. Whatever the case, they're doing a good job if there's mass deletions going on (no offense, OP).