This happened to me recently twice to be exact, both timers didnt go off but the alarm is on the screen and yet no sound at all. Im using iphone 13 pro with the newest ios update. I tried the alarm too and its the same no sound but it will show it on the screen.
Also my bf have been having this issue for 2 years now with his iphone 12 at first I couldn't believe it and said hes just a heavy sleeper thats why he couldn't hear his alarms at all lol
Now he switched to the newest iphone model and he hasn't encountered it yet.
For video and subscriptions (cause my bf got it for me and hes using apple too). I like going to concerts and vid quality of apple is good but now im thinking of getting the other one for zooming quality for vid ๐