Hi,
have you tried that cc#7 with expression pedal A?
I have 3 FCB:s and I have get only ones expression A pedal working with KPA wheter programmed equally ( )....different kind of problem as your -but mine B is working, doesnt matter is it vol or wah...
strange machines..
For sure: you havent any other volume pedal connected to Kemper? There could be only one at a time.
And that "module is empty" notification seems like your pedal is sending wrong cc... Some cc -number of stomps or effects..Just thoughts..
-Olli