I just think that with the vast amounts of compute involved and the tendency to reward hack, we can't assume the steps towards that formalization are without error until full human understanding of the formalization.
I'm unaware of any serious proofs that have been shown to have a kernel exploit in them.
I agree with Jtarii that it's very unlikely a Lean bug is critical to most of these proofs. But we're in strange times, so I agree wtih the sentiment that we should wait for further analysis before declaring complete confidence in the proofs.