I have quite a few servers with hetzner. I don't know what the exact criteria are but once you hit around 250TB/month per server with multiple servers for (likely) multiple months in a row then they will tell you to chill out or they will terminate. I've gotten it and I've seen a few others on lowendtalk mention it too.

I've been using hetzner for a couple years and have always used them for my high bandwidth services but I have only gotten that notice once despite being a very heavy user, and around the same time everyone else did around a year ago. Maybe they're gonna start to care? With all the price hikes and all. I ended up just getting more servers to level it all out.