To be clear, I'm not saying a one sentence Slack message can't be ignored. I've coached these folks about how they might need to make multiple attempts to get someone's attention and they're always receptive.

But that's very different than when an engineer stays up all night investigating a very serious issue, writing it up completely, and offering multiple solutions in a wall of text that can't be brushed off in Slack. The engineer makes multiple attempts across multiple weeks and communication platforms to get their attention, and it's ignored. Not "we're busy but will get back to you when we can." Just completely ignored.

A high performer (and really anyone) should not have to resign themselves to office politics to workaround this kind of dysfunction. It's imperative to fire such managers so that you don't lose the trust of the people doing the work.