n the spirit of "self-help," I went to BestBuy and bought a new Samsung Galaxy Tab A6 (for a little over $100). They also sell DJIs. The sales clerk assured me that it would work and sure enough it did work (after turning on the USB debug option). It is even an improvement in that it is 7" vs. the older tablet's 8" size, so it can fit in the controller arms, no need for a support accessory.
From this I can only assume that the original Android 5.0.2 operating system is not compatible with the Mavic Pro controller.