Discouraging that this still is an issue. My iPhone 10 pro iOS 15.5 has been a problem with volumes since iOS13. My volumes are a mess. In Settings, Notifications, Messages my volumes are different from the Settings, Sounds&Haptics, Text Tone. That is, with sliders at max the same tone is a different volume in the two settings locations. What's worse is only some of the Messages volumes are different. Every week I miss a few calls or texts because the volume is too low and I don't hear it on my desk in front of me when the side buttons are set to full volume. It seems like they are changing and I can't figure out why. Maybe there are too many volume control points in the system.