I have four units and they were canceling each other out. LINE 6 solution: power down all the unites then insert the first transmitter into the first docking unit. Let them connect. Then follow up on the remaining three in the same succession. None of them work now.
What we noticed is when we power up another unit all the ones before blink. Telling us they are recognizing the new addition but we think they are changing channels to match the newest addition and perhaps that is why they are canceling each other out.
But your solution is different: you say "after" docking the transmitter into the docking unit "then" plug the transmitter into the guitar BEFORE powering up the other units to allow the first unit to hook up. THEN repeat the same process for the remaining three. When the transmitter goes into sleep mode does it continue to keep the same channel after waking up or do I have to repeat this process every time the band returns after a break?