Mine was doing that for the past couple days, too. (even after a re format) I figured maybe the rear camera cable was loose, but apparently not.
I replaced the memory card this morning with a Sandisk Extreme 256gb u3 card, and it hasnt happened once today so far. Perhaps it had something to do with the speed of the old card, combined with 1.9?
Ill let you know if it happens again with the new faster card. Before, I had a regular A1 Sandisk 256gb card, which has been in there since December 19th or so.