Plenty of people have reported problems with missing alarms associated to locked or rebooted phones. My problem is different:
- I just started booting the phone (after the battery was dead), but left it on the SIM unlock screen.
- One of my scheduled alarms went off (with a stock sound) - helpful.
- I unlocked it and booted the rest of the way while the alarm kept going, but found no way to dismiss/stop it; no notification appeared, the Dismiss buttons in the Alarm app did nothing (I think those were anyway only future alarms). Only thing that worked was rebooting the phone again.