Years ago, I bought a used Ground Control Pro. When I hooked it up to my Mesa/Boogie JP-2C I realized that it didn't switch the JP2C at the first startup attempt. As soon as I unplugged the midi cable from the GCP and inserted it again, the amp started to respond. I figured there was something wrong with the GCP, and simply bought a brand new one
That one, however, acted the same way. I decided to live with it until a few days ago when I had re-arranged my rig with additional midi gear hooked up in series before the JP2c. I got up on stage at a major festival, and the rig wouldn't switch for 15 minutes. It acted in a similar way on the rehearsals the days before, but it started working quicker. As soon as it starts working, it works until I DISCONNECT the cables. I can turn the rig off and it will work perfectly well when it's turned back on, but if the cables are disconnected in between two sessions, the problem comes back.
Is there any MIDI magician here that understands what's going on?