Why does my ringtone volume get set to low?

[AC Question]

Android 5.0, Galaxy S5. Verizon Service.

I manually set the volume almost as loud as it will go. Something is resetting the volume to low. I have read that 5.0 has bugs, is this one of them? Can this be fixed? I have no idea at this point what sequence of events occurs before the volume gets reset to low. TIA for any help
Bob Helms