Today is day 2 of doing the button sequence that Steve Z suggested. Not a single lock up on any of the 3 E4K units in our house. That button sequence might just be the trick. Not sure what it does, but since you don't lose anything, it might be a secret way of turning off whatever is causing the screen freezes.
So to repeat so you don't have to go look for it. you pressed the following buttons the number of times shown in the sequence below.
Home - 5
Up - 1
RR - 2
FF - 2
Then just wait. The Roku menu with go up and down and eventually stop at Settings. Then it just sits there for quite a few seconds before the bouncing Roku logo comes up. Be patient, it will appear. When whatever it does is finished, it takes you back to the Roku Home Screen. Mine looked a bit different. The icons looked simpler. But I really did not pay attention. You might want to snap a photo of your icons on the home screen before doing this and then compare that photo to the icons after the reset. Could have been my imagination.