When I go to streaming Channels and scroll to apps the page is blank, this started 3 days ago. I can still cast from my iPhone.
These things are just special purpose computers, and just like their big brothers, sometimes operational problems cans be solved by a system restart.
From the Roku home screen use menu path Settings > System > System restart. (On a Roku TV the menu path is Settings > System > Power > System restart.)
If the problem you're having doesn't let you control the Roku via the remote, you can restart by pulling the power plug for 30 seconds or so then plugging back in.