I tried your suggested fix of deleting a channel, rebooting the tv and then reloading the channel, in that order and regret to advise no improvement at all. At first it didn't want to even reload the deleted channel (sling) but after a few tries (changing nothing) it did.
The big question for all of us ROKU users is how is it possible for an international company of ROKU's size (S30 billion) to send out a software update that clearly doesn't work without the ability to go back to the previous software version until the new one is sorted out? I guess I am "lucky" in that I can still view programs after waiting about a minute for a channel to load and then another minute for the individual video to load after that. Time to make tea between selecting a video and having it appear on the screen.
Perhaps this is why ROKU's stock market price has halved in the last four months.