With the iOS 11 update, Alarm volume seems to go extremely low even when the user have tried to set it maximum manually. User can’t seem to control alarm volume and alarm rings very low. It says volume all the way up but alarm is still very low.
Fix : Check “change volume with buttons”
The “Change with button”-setting may have get resetted to default off state after major upgrade. I had this same issue and just figured out how to fix it. In settings go to sounds, There you can adjust the ringer and alerts volume or turn on “change with buttons”
Once done in the sound settings you’ll see “Ringer and Alerts” where you can adjust your alert volume. This has resolved problem for almost all user facing the issue of very low volume of alarm even if set to maximum level.