Rando10 Curious if this is an issue with anyone else?
Made same observation (at Pixel 8 (no pro)). Sure to have missed some alarms + observed with clear mind when I began to become suspicious. Not sure under which conditions it exactly fails (maybe after letting auto-reboot end secondary user session, even if alarm is correctly setup in both secondary and owner profile ??); couldn't pinpoint enough, yet.
Personal "workaround": Most often I actively end secondary user session before bed - this seemed to mitigate the problem. (Not properly investigated, whether this is really technically solid or mere wishful thinking, though.)
Nonetheless and IIRC your error description seems consistent with my cases. (Had changed alarm tone as well from default tone to one of the other built-in ones.) Thanks for bringing it up!