Phil! You guessed wrong but its not forbidden. Last one is expression, one is volume boost assigne to a footswitch and thirs is another gain to balanced things up because I was probably lazy in this case. The minute Ii loose the 2B path my patch turn silent because I've set the output of 2A to -120 dB to make it obvius. Then I check Y A/B and it still indicate B 100%, it is activated, such nothing I can do to bring it back to life. And! It's reproductible.
Copy a similar preset to 4A, 4B, 4C and 4D for exemple. After copying 4D, the 4A, 4B and 4C will be silent forever. To get 4D to work again you need to select a blank New preset in 5A and then back to 4D.
No quite what you want for a gig.