Behaviour of the Watchdog Timer on Ubuntu Core

I have noticed some inconsistencies on Raspberry Pi CM4 running core20 and core 22.

I am investigating the behaviour of the hardware watchdog. I use snap set core watchdog.runtime-timeout to a non zero value (less than 15s) set the runtime watchdog. I am observing the watchdog taking effect and restarting the system in the event of a kernel panic. This seems to work both on the core20 system and the core22 system.

However if I set the value back to 0 to disable the runtime watchdog, there are differences between the behaviour on core20 and core22. One core22 the system does not restart in the event of a kernel panic. One core20 the system does restart in the event of a kernel panic. Can anyone explain what is going on in the core20 system compare to core22?

this is most likely a bug in snapd or in its communication with systemd, can you open a launchpad bug for this against snapd ?

while there are some watchdog tests being run, in the certification lab, i don’t think randomly turning it on and off at will is one of them.