I am having the same problem on two devices. One has roku built into the smart TV the other is a roku device plugged into a TV. In both cases I have check that there are no system updates needed, i have done a network check and have removed quite a few channels from each device. I have powered off each device as well as the routers each is connected to. One is wireless the other is wired.
What is going on. Is roku getting hacked?
You didn't say what app you were trying to play, so I tried Prime Video. It's working like a champ.
Now, what you've done seems like proper steps, and you're still not getting some app to run. So, what is the app? And where are you (state/country)?