See this is the stuff I LOOOOVE LLMs for, it assembled all this without me having to dig forever:

18:49:20 nova-compute: "Rebooting instance after nova-compute restart.", then it waits for network-vif-plugged. The guest is paused. https://zuul.opendev.org/t/openstack/build/4b61b567c72e4027a23b7c330ab23e0d/log/compute1/logs/screen-n-cpu.txt#18782
18:49:20 nova-compute: "Rebooting instance after nova-compute restart.", then it waits for network-vif-plugged. The guest is paused. https://zuul.opendev.org/t/openstack/build/4b61b567c72e4027a23b7c330ab23e0d/log/compute1/logs/screen-n-cpu.txt#18782
18:54:21 nova-compute: "Timeout waiting for ['network-vif-plugged-...'] ... timed out after 300.00 seconds", then "Failed to resume instance: ... VirtualInterfaceCreateException". The server goes to ERROR, power state Paused. https://zuul.opendev.org/t/openstack/build/4b61b567c72e4027a23b7c330ab23e0d/log/compute1/logs/screen-n-cpu.txt#19072
18:54:22 nova-compute starts its RPC servers, and gets the same event (same request ID as the 18:49:23 POST): "Received unexpected event network-vif-plugged-...". https://zuul.opendev.org/t/openstack/build/4b61b567c72e4027a23b7c330ab23e0d/log/compute1/logs/screen-n-cpu.txt#19190