right, so I returned the device used above, and waited a few months, only to experience a power out the other day…
so, I ordered a new UPS, and lo and behold, within minutes of installing it, the same loggings returned
this must be a fluke, and the first thing I did was edit the automation to Not issue critical warnings on that anymore.
in the device dashboard, the only entity I could find that was out of the regular, was the battery chemistry (sensor.ups_chemie_van_de_batterij in Dutch) having no value/state. I saw it getting back to PbAc later on.
Maybe that is some sort of selftest in the Integration/Add-on.
to be able to what the history of some of the important entities, I now enabled them in the recorder, maybe that will show problems if and when the next notification is issued…
I do see this
but these times dont coincide with any notification I got…
update
raised issue in HA repo