Recently a lean formalized proof of the Collatz conjecture had exploited bugs in the lean kernel. However, the kernel is fairly small so hopefully it'll be bullet proof soonish.
It should be noted that it wasn't a legitimate attempt at the collatz conjecture. Someone found a lean bug and created the proof to show it off. It wasn't an llm reward hacking (but this still is a concerning risk). Lean probably isn't the best kernel for adversarial proofs, but it probably has too much momentum at this point for anything else to take over.
