Contacted DA, and they suggested that rebooting "is usually a sign that the unit is not communicating fully with the power bar." Their suggestions were 1 - power off the power bars(s) so the system is completely powered down, then restart, and 2 - change the port on the power bar that the head unit is plugged into to see if that re-establishes communication. I did both, but no luck. I removed all the modules, and verified the firmware of each. Checksums didn't match, so I reloaded the same firmware starting with the PB4 first. That did the trick. Weird, because nothing had been changed.