So I had the same issue described above with the Nav losing the satellites and black screen on reverse - this was about two days after the dealer actually finally updated the software on my infotainment. Searching through various posts I saw a note about disconnecting the ground/battery negative lead. Curious I decided to try it. I can say that initially I was worried i had screwed the system as all the functionality that was originally there was gone.... ventilated seats, power step, Sirius etc... well patience was my friend and when I got in the truck the next morning everything was restored - and strangely it was slightly different. I don't know if the software that was updated had fully taken or integrated with every other onboard system, but i'm guessing that might have been the case. Anyway to cut a long story short everything seems to be working as intended. I did need to restore some settings that had been defaulted but the Sirius stations were all there (associated with key fob). In all it was worth the 5 minute job of undoing the battery terminal, and overnight wait
If it does it again however I will be trading this early 2019 MY (05/18) for a 2020 because everything else rocks.