The fact that a later Kernel versions work fine _could_ be because of a hpwdt commit after 5.10: https://github.com/torvalds/linux/commit/acc195bd2cc48445ea35d00036d8c0afcc4fcc9c#diff-994ee4b010b5c6222ad7a20e160f733401f46894b36fa3e1fb6ffbb48bedb817 I have not tested sid or a newer Kernel on our HP machines though. If you've compiled your own Kernel and this one works (did your do a multiple reboot test?), maybe there's a difference in the Kernel "config"?
What happens if you disable the hpwdt module as mentioned in the other bug reports? Does Bullseye with 5.10 and experimental with 5.14 work in this case?
