This is the scenario: 
Normally I'm paired only with my wife's 20S, as intercom n°1.
Sometimes I add a friend's intercom using the Universal Intercom Pairing.
So my friend is the new n°1 and my wife becomes n°2 (I know this is the designed behavior). No problems in this situation. 
Then I change the order with the App (wife n°1, friend n°2) and save it to the device. Here is where the mess begins!

If I tap twice the intercom button, I can talk with my friend. But if I tap it once I can talk with my wife only a few times: most of the times the voice says "Intercom error". Same thing if she tries to open the connection. And when we are able to talk, sometime we hear in low quality, sometime in high quality...