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.

Soon.

That is correct.

Hello, Please open a ticket at https://go.netgate.com, Please provide the serail number of the unit that is not working, we will be able to take a look see what we can do to help you out.

In reference to: You think they'd have tested this on Netgate hardware.
We do, extensively, it sounds like there might have been a physical issue causing this problem (bad RAM, storage or other board level component died).