DIAGNOSIS The TV's internal storage is full of cached app data. Roku OS and channels share a small partition.
FIX Go to Settings > System > Power > System restart. This clears temporary cache. Then go to Settings > System > Storage and check space. Remove any channels you don't use.
IF THAT DIDN'T WORK You need to clear the cache for large streaming apps. Go to the Home screen. Highlight the problematic app, press the Star (*) button on the remote, and select "Remove channel." Then add it back fresh from the channel store.
HEADS UP Never "force stop" apps from the settings menu. It can cause system instability. Always use the Remove/Re-add method.