I am sure it is a Cardo Garmin compatibility problem that neither side wants to take seriously. I had a Sho 1 for two years with nothing but frustration.
Just swapped to a Sena 20S and wow, perfect, no stuttering music, no music 'jamming' and when I leave the bike for a couple of minutes then jump back on, within 60 seconds the Sena has reconnected perfectly. Even the multi inputs seem to be no problem i.e Music playing - Nav instruction - music restarts - phone call taken (iPhone) - music restarts on completion of phone call.
Wished I had bought one two years ago!