Thanks for the quick reply. This was with one of our Ultras and just happened tonight (the 2nd time) on the same unit we noticed it with before. This is by far our most watched unit and relatively new (May 25th). If it happens again I'll try swapping the PS since there's no sd card.
If it's really only happening on one device, if you bought it from a big box store, Walmart, Target, Meijer, etc., with a 90-day return policy, I might be inclined to factory rest and return it as defective, and buy another one. If it's outside of the return policy of where you bought it, you could contact Roku for a warranty replacement.