I think adding if failed host 127.0.0.1 port 3493 type TCP then restart to /etc/monit/conf.d/openmediavault-nut.conf will do it. Can you check that?
After that you need to run systemctl restart monit.
I am back from training today.
I updated OMV-update and got openmediavault-nut 5.0.3 today.
Then I saw the comment above and and added the line.
I restarted "systemctl restart monit" as directed.
Now time will tell: even with my workaround checking every 5 seconds, I still got random stops/recover starts every 3/4 hours or so, so only 6/7 notifications extra per day instead of 300, which is good.
That is also after updating to openmediavault-nut 5.0.2: by the way, very elegant leverage of monit: I'd done that after your suggesting, if you had not already right away in 5.0.2 .
I noticed now that after openmediavault-nut 5.0.2/3 updates I am occasionally getting a different error message.
Quick question: should I stop my workaround script to see if your fix worked, or should I leave them working in tandem (together)? I think right now it is a tad overkill running with your 5.0.3 fix + the code fix above + my workaround script all at the same time, which should I stop, if any?
PS: thank you so much for taking care of this so quickly and with official updates: I am really honored.