@Guderian It's nothing to do with Nowtv as the Pluto app doesn't work on my Roku either. They just host the app. We just have to wait until Pluto TV fix it.
@Guderian The TuneIn radio app stopped working a few weeks ago and they fixed it pretty quickly. So fingers crossed Pluto works fully again soon as it has some interesting stuff.
Seems Roku users over in the USA and other Countries are encountering problems with the Pluto TV channel (App) plus other channels (Apps) since a recent Roku software rollout.
More information here if you fancy reading the thread on the Roku Community Forum.
For me Pluto TV has been hit & miss with regards to opening and using the App.