My six month old Roku Ultra freezes up constantly. On the home screen, no app is highlighted and no navigation is possible. Any button pushed on the remote just causes the sound normally made during navigation, but nothing happens. There is no way to navigate anywhere: Apps, Settings, nowhere. The only way to use the Roku again is to unplug and restart the Roku, but it just freezes up again after using. I used a stick for years with no problems. Definitely sorry I made this "upgrade"!
Roku operating system version 10.5 added added a new "Power" item in the "Settings > System" menu for some of the newer Roku devices. The new "Auto power savings" item there will put your Roku device into a low power standby condition after a period of inactivity, such as when your tv has been turned off for a while.
Pulling the power for a few seconds to restart the Roku will restore full operation.
If you have a "Settings > System > Power" menu item, deactivating any power saving options you find under "Auto power savings" will prevent your Roku from going into standby in the first place.