I ran into the exact same bug (with the same error messages Vladislav noted) on my Raspberry Pis running the latest version of Pi OS Bookworm (downstream from Debian).
I had triggered a self test just before doing an end-to-end test of the UPS configuration, and my Ubuntu servers running 20.04 all shut down, but my Pis running Debian 12 did not, due to this bug!
