This issue should of been resolved in v7.30 of Plex for Android which is currently in beta, you can sideload the build from: Release Announcements - Android TV beta or join our beta to access the build via Google Play.
If your still having problems in the new player, would you be able to grab the client logs and I will take a look. Information about grabbing the logs is available here; https://support.plex.tv/articles/201573117-android-android-tv-fire-tv-logs/
