Instance can't be restarted - Error in the logs shows "cannot acquire state change lock (held by monitor=remoteDispatchDomainBlockJobAbort)"

Issue

A failed operation like a snapshot on the instance can leave it in an unresponsive state.

If you try to hard reboot it you can see the following error in the logs:

2021-01-20 10:38:04.111 8 INFO nova.compute.manager [$req - default default] [instance: $instance_uuid] Rebooting instance 
2021-01-20 10:38:34.559 8 WARNING nova.virt.libvirt.driver [$req - default default] [instance: $instance_uuid] Cannot destroy instance, operation time out: libvirtError: Timed out during operation: cannot acquire state change lock (held by monitor=remoteDispatchDomainBlockJobAbort)
2021-01-20 10:38:34.567 8 WARNING nova.compute.manager [$req - default default] [instance: $instance_uuid] Reboot failed but instance is running: InstancePowerOffFailure: Failed to power off instance: operation time out