Well no issues with a different phone, got it setup without any reboots. The issue seems to be the edge sensitivity and how you hold the phone. Sometimes you end up pushing the volume buttons and performing an edge squeeze, the later seems to take precedence, as per the visual feedback and the fact the volume doesn't increase. So a work around would be to decrease the edge sensitivity, which is in the options, or just turn if off completely.
On a side note the audio output is bloody good, I still have a V30+ and was holding on to that for the quad dac and the wide angled lens but I would be more than happy listening to tunes on the U12+ and usonic earphones.