iPhone randomly changes ringtone and alarm sounds. Please help

My iPhone keeps changing my ringtone and alarm sounds. I have an iPhone 12 mini, running iOS 18.7.1. This has been happening for more than a year. My alarms and my ringtone are set to (different) “classic” iPhone sounds. But randomly when they go off, they’ll use a different tone, often the iPhone default. When I check what the alarm or ringtone is set to, the setting hasn’t changed from my preferred tone. Changing off it then changing back to the preferred sound fixes the problem for a little bit, but a few days later it will have the same problem. I’ve missed phone calls because the phone isn’t using my ringtone. I’ve been using these sounds for more than a decade without a problem, until sometime last year something in iOS broke. The classic ringtones exist on my phone and they play when I click on them. I’ve restarted, I’ve closed apps, I’ve recreated alarms, and I’ve updated iOS throughout the year (at least prior to 26, and I don’t see anything about this in release notes). I’m at a loss and extremely annoyed. Can anyone please help?