Eh, that's nothing, few friend of mine had issues where Android would sometimes not ring alerts. Why? Who knows, maybe some weird bug that manifested itself in some combination of system settings and phone firmware.

I have multiple devices so I usually set alert on home phone + work phone if it's something really important like a flight at 6 AM; but if I were to use an alarm clock everyday I'd probably buy the simplest one I can find for few bucks.