It might be. I never had an issue with this on my previous OnePlus phone (which at least at the time was pretty close to stock Android), but I was stumped to se

It might be. I never had an issue with this on my previous OnePlus phone (which at least at the time was pretty close to stock Android), but I was stumped to see that the Google Clock alarm was not going off multiple nights (seemingly at random) on my new Huawei phone. Turns out the phone was closing the app in the background due to it running for a long time... huh. Switching the the built-in clock app (it's whitelisted, probably) fixed the issue, though it's not a good user experience. (To note: there is a settings screen to override per-app background closing behavior, but for an alarm clock I don't mind so much which app I end up using.) It is pretty annoying still having the whitelist e.g. VPN apps manually whilst travelling as the phone was closing them constantly.