This same error may get displayed for different issues. It is best to provide Plex for Android logs from the Amazon Fire and from the server so they can be checked out
See
https://support.plex.tv/articles/201573117-android-android-tv-fire-tv-logs/
https://support.plex.tv/articles/201643703-reporting-issues-with-plex-media-server/
https://support.plex.tv/articles/200250417-plex-media-server-log-files/
