Well that's strange. The a/c units in your coach don't know the difference between genset and shore power, so something weird must be happening. I'm pretty sure your coach has an EMS that manages power loads when connected to only 30A shore power. It may have mistakenly "shed" (dropped out) the mid a/c unit. It turns itself off when the genset runs, but stays active if it thinks it is using 30A shore power. Try turning off the main battery disconnect for 20 seconds. That should reset the EMS and might bring the a/c back on.