There was a volume issue with the release of 3.12 in May.
See 3.12 Firmware
And search for volume in the thread.
Also see Critical Safety Issue: Naim Atom Unity Volume Jumps to 100% After Latest Firmware Update
This was and apparently again is a serious issue!
I suffered from it myself in May and it scared the hell out of me. I was only able to reach my volume knob when it already was in the 12 o’clock position rapidly going to 1 o’clock whereas normally I play at a maximum of 8 o’clock 
. I wanted to cry for my loudspeakers but was unable to because of a heart rate of 180+… I did not touch the Naim app for two weeks after the issue had been resolved with a software update that took almost a week to pass Google.
At the time the cause of the issue stemmed from the device mistakenly thinking multiple button presses are “press and hold” which causes the volume to max or min.
Perhaps someone at Naim needs to take another look?