I have a Kemper PowerHead with FW 3.1.4.
I've noticed a very strange behavior regarding the master volume.
If you turn the master volume from 0 to something like 3 and back to 0 repeatedly times, you will notice a volume drop each time you do that. You can hear that the sound will remain cut off until later in the volume number. For example, for the first time the volume at 0.1 will already have some sound, next time only at 0.3, then 0.7, then 1.0, and so on.
I had to turn off and on my kemper to restore the normal behavior in volume.
I was using the internal power amp. Don't know if it will happen to the studio main outputs.