That file could only be stuck if somehow the notifyqueue_running lock is stale or not being released. Maybe something in your notification settings is broken and it can't get messages out.

to me the problem should be investigated on the vm side more than from inside pfsense. i see on google that people tend to bridge the interface instead off using the passthrough for unraid. personally, for example, i was never able to make pfSense work reliable under virtualbox and i had to change the vm to qemu/kvm