Yes that’s the issue (or at least one of them) I’m definitely getting - these unknown alarms or notifications often come through with audio alert at maximum volume - so either bypass volume control or max it out - AND there’s no way to stop them when they happen because there’s no visible alert to tap or such… (and it happens to my ring volume occasionally for calls too).
EDIT: FWIW I just had a similar experience with a pair of SMS messages - details in other thread, but very very much the same:
Also - I’ve noted I found couple of apps (e.g. ioDroid) that have what appear to be new or additional notifications now that they may not have had back pre-7.7 (i.e. F-Droid vs. what ioDroid now has)?