No one at the dealership, nor on this forum, has had any experience with this completely random failure. It has continued randomly for the last two 1/2 weeks. There is no pattern that I can discern; sun position, time, temp, location, etc.
Two hours after I dropped it off, dealership calls to say that GM has had some prior experience and they recommend changing the fuse box. Yep, the entire thing. Whatever! I'll let you know if it works.
OBTW: covered under warranty