Appreciate the reply.
Have you tried the suggestion posted by @Plex_OnRoko? If not, we suggest giving it a shot. If the issue persists, removing the Plex channel and then reinstalling it may help. To ensure the process is successful, restart your device before adding the channel back in. We would recommend doing this from the Settings menu by navigating to Settings > System > Power (If you do not see a Power submenu, skip to the next step.) > System restart.
For detailed instructions, refer to this Support link: How do I resolve channel playback issues?
Keep us posted!
All the best,
Roku Forum Moderator