Today I updated and rebooted a bunch of servers - all in a day's work. Everything went fine, until one of the hosts (the big one) didn't boot up again properly.
I've got two hosts, both running ProxmoxVE (version 7.1) and Microsoft Defender for Endpoint (version 101.61.69-insiderfast). On reboot, one of the hosts came up fine; the other didn't.
Long story short, uninstalling mdatp fixed the problem - wild hypothesis, but I suspect it was interfering with either network bridge or interprocess communication.
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