Having the same issue on one channel "Tubi" One movie no volume, the other lost video but kept sound. Tried the unplugging and no joy. Also I have tried going on other apps and there is buffering and the screen freezes.
Thanks for the post.
Try removing the channel from the Roku home screen by navigating to the channel tile, pressing the * key on your remote and choosing 'Remove channel'. Then restart your device from Settings>System>System restart. Once your player starts up again, add the channel back once more. Does this clear up the issue you are seeing?
Thanks,
Danny