A couple of My premium channels will open but then close and exited to home page of ROKU

A warm welcome here at the Roku Community, BarbaraG1!

Thanks for reaching out to us regarding your playback issues with certain apps. Worry no more, as we are more than happy to assist you with this. 

Have you tried to remove the affected app, perform a system reboot, and then reinstall the app? If not, kindly follow the steps provided below:

1. Remove the affected apps by highlighting them and pressing the Star (*) button
2. Restart your Roku device/TV from Settings > System > Power > System Restart
3. Reinstall the affected apps again. Select Channel Store > Search for the app > Click Add channel

We need to make sure that this process has been done precisely to work. Furthermore, if the issue still occurs, let us know, and we'll go from there. 

Kind regards,
Carly