I think I figured out that the rig changes but the cab doesn't. Let's say you start with rig1 and switch to rig2 via MIDI. I made some tests and the faulty rig (rig2) sounded like rig2 with the cab from the rig you selected first (rig1). I checked this by locking the cab which resulted in the same sound as when changing the rig via MIDI.
If you start with another rig (by selecting by hand at the Kemper or with Kemper Remote) then this cab is used for the rigs you select next.
In the display, it shows the name of the cab which should be selected, but it doesn't sound like this cab.
Can someone confirm this?
I have this midi bug too.