The most recent and egregious example would be banning users who run cryptocurrency-related nodes, even if not mining, despite only mining and similar activities being prohibited in the ToS. Here's a reddit comment from the official account stating that trading is also prohibited: https://old.reddit.com/r/hetzner/comments/wucxs4/is_it_allow...
While banning mining is perfectly understandable (the data centers are likely built around an assumption of normal usage patterns and not 100% CPU 100% of the time, and at least one cryptocurrency is infamous for wearing out SSDs with its mining), banning trading bots, proof of stake, and the operation of nodes for blockchain analysis is extremely surprising, even if you have read the TOS. And like in the earlier cases I've heard about, the servers seem to have been blocked without warning.