In my case, the way this “scheduled alarms fail” bug manifested itself had nothing to do with the “no sound” issue. It was not just the alarm sound missing but there was completely NOTHING happening - not even the alarm popup (dialog / notification) shown. Then, after the snooze period (that I have set to 10 minutes) a SILENT notification was shown on the Events screen about the SNOOZED alarm that I never snoozed. And then, another 10 minutes later (i.e. 20 minutes past the scheduled time), the alarm eventually went off with all its sounds and notifications.
So it was definitely something completely different than the famous “sudden lack of sound” bug.
(Un)fortunately, since then I haven’t seen it again, so I couldn’t further investigate it.