iPhone X Alarm Doesn't Always Sound

I have had an ongoing issue that started with my iPhone 5, continued with 2 different iPhone 6's, and now with my iPhone X. Sometimes, seemingly at random, the alarm won't sound. The phone shows the alarm going off but no sound is produced. I have reset my settings, I have reset my phones, I have restored my phones, and I have set up my phones as a new phone. The issue continues. For example, without any changes to the settings, the alarm will work as it should one night, the next night it won't. The third night, it will work again.

Has anyone else encountered this problem? I believe the problem is created through some kind of glitch with notifications or alerts. It obviously is not a phone issue, but a software or iCloud issue.