100 % master volume does not equal 100% device volume.
100% master volume is the setting of the actual device volume.
Is that intentional?
It's not really a bug or a feature, but a limitation of the mobile device. Apps can't change the mobile device's volume, only the volume of the sound they output to the device. But if you set your device volume to 100%, then adjusting the output volume in the app will give the same result.
Thanks, that's not ideal, but it is as it is.......