And then they don't respond to email or slack. Are they missing it? Ignoring it? No one knows. Meanwhile, time sensitive deadlines come and go.

There's no clear, easy protocol that works for everyone, unfortunately. Some people are always going to operate on the 'better to ask forgiveness than permission' model. And I say this as someone who is often in the 'always busy' camp.

If it’s on the record then it would be simple to assign blame on them for the consequences… and then punish accordingly, so it seems like a self correcting issue?

Most employees probably have enough credibility to explain away one or two missed deadlines, but not 5 or 6 in a row without providing actual proof.