Could not tune channel. Please check your tuner or antenna

Would need Plex for Android logs for this to go with the Plex Media Server logs

Looking at one of the Live TV sessions
Tuned channel 4.1 at 10:05:52 on 23rd March

Last server action was returning a transcoded segment to the Fire TV Plex app

Mar 23, 2021 10:13:55.289 [20964] DEBUG - [Transcode/db8773dbc7d1f48c-com-plexapp-android] Asked for segment 434 from session.

Mar 23, 2021 10:13:55.289 [20964] DEBUG - [Transcode/db8773dbc7d1f48c-com-plexapp-android] Returning segment 434 from session

Next was the Android app stopping the stream

Mar 23, 2021 10:13:55.584 [31136] DEBUG - Request: [192.168.0.151:52956 (Allowed Network (Subnet))] GET /:/timeline?airingID=19906&audioStreamID=40336&duration=394994&guid=plex%3A%2F%2Fepisode%2F604a5d13b3452d002c21f3dc&key=%2Flivetv%2Fsessions%2F11be4a7a-c486-4309-b5e4-e1348efd539e&playbackTime=475098&playQueueItemID=4.1-1616511600000&ratingKey=17219&state=stopped&time=386986&token=xxxxxxxxxxxxxxxxxxxx (29 live) TLS GZIP Signed-in Token (deerewright)
Mar 23, 2021 10:13:55.584 [31136] DEBUG - Client [db8773dbc7d1f48c-com-plexapp-android] reporting timeline state stopped, progress of 386986/394994ms for guid=plex://episode/604a5d13b3452d002c21f3dc, playbackTime=475098ms ratingKey=17219 url=, key=/livetv/sessions/11be4a7a-c486-4309-b5e4-e1348efd539e, containerKey=, metadataId=17219, source=
Mar 23, 2021 10:13:55.586 [31136] DEBUG - [Now] User is deerewright (ID: 1)
Mar 23, 2021 10:13:55.586 [31136] DEBUG - [Now] Device is Android (AFTMM).
Mar 23, 2021 10:13:55.586 [31136] DEBUG - [Now] Profile is Android
Mar 23, 2021 10:13:55.586 [31136] DEBUG - [Now] Updated play state for /livetv/sessions/11be4a7a-c486-4309-b5e4-e1348efd539e.

For Android App log see Android, Android TV, Fire TV, Portal Logs | Plex Support

Would need corresponding server and app logs and indication as to when the live tv session was started and when it failed

Suggesr waiting for version 8.15 of the app if not available yet and reproduce with that or a later version (release note: Plex for Android - #380 by marekszulik)