@Mothy_Tim
I see your logs and a transcode session starting, Thank you for posting 
Here, I can see it looking for the Hardware but not finding it.
Did you forget to passthrough in the container definition ?
Dec 19, 2021 16:47:02.686 [0x145f7257cb38] DEBUG - [Transcode] It took 10.000000 ms to retrieve 120 items.
Dec 19, 2021 16:47:02.694 [0x145f7257cb38] DEBUG - [Transcode] It took 0.000000 ms to retrieve 120 items.
Dec 19, 2021 16:47:02.696 [0x145f7257cb38] DEBUG - [Transcode] We're going to try to auto-select an audio stream for account 1.
Dec 19, 2021 16:47:02.696 [0x145f7257cb38] DEBUG - [Transcode] Selecting best audio stream for part ID 54427 (autoselect: 1 language: en)
Dec 19, 2021 16:47:02.696 [0x145f7257cb38] DEBUG - [Transcode] We're going to try to auto-select a subtitle.
Dec 19, 2021 16:47:02.696 [0x145f7257cb38] DEBUG - [Transcode] Audio Stream: 117182, Subtitle Stream: -1
Dec 19, 2021 16:47:02.699 [0x145f7257cb38] DEBUG - [Transcode] MDE: Selected protocol hls; container: mkv
Dec 19, 2021 16:47:02.699 [0x145f7257cb38] DEBUG - [Transcode] MDE: analyzing media item 52487
Dec 19, 2021 16:47:02.699 [0x145f7257cb38] DEBUG - [Transcode] MDE: Gremlins 2: The New Batch (1990): Direct Play is disabled
Dec 19, 2021 16:47:02.699 [0x145f7257cb38] DEBUG - [Transcode] MDE: Gremlins 2: The New Batch (1990): media must be transcoded in order to use the hls protocol
Dec 19, 2021 16:47:02.699 [0x145f7257cb38] DEBUG - [Transcode] MDE: Gremlins 2: The New Batch (1990): no direct play video profile exists for http/mkv/h264
Dec 19, 2021 16:47:02.699 [0x145f7257cb38] DEBUG - [Transcode] MDE: Gremlins 2: The New Batch (1990): no direct play video profile exists for http/mkv/h264/dca
Dec 19, 2021 16:47:02.701 [0x145f7257cb38] DEBUG - [Transcode] MDE: Gremlins 2: The New Batch (1990): selected media 0 / 52487
Dec 19, 2021 16:47:02.701 [0x145f7257cb38] DEBUG - [Transcode] Streaming Resource: Reached Decision id=48447 codes=(General=1001,Direct play not available; Conversion OK. Direct Play=3000,App cannot direct play this item. Direct play is disabled. Transcode=1001,Direct play not available; Conversion OK.) media=(id=52487 part=(id=54427 decision=transcode container=mkv protocol=hls streams=(Video=(id=117181 decision=copy width=1920 height=1080) Audio=(id=117182 decision=copy channels=6 rate=48000))))
Dec 19, 2021 16:47:02.703 [0x145f74c14b38] DEBUG - Completed: [10.19.64.64:44350] 200 GET /video/:/transcode/universal/decision?audioBoost=100&autoAdjustQuality=0&directPlay=0&directStream=1&directStreamAudio=1&fastSeek=1&hasMDE=1&location=lan&maxVideoBitrate=200000&mediaBufferSize=209664&mediaIndex=0&partIndex=0&path=%2Flibrary%2Fmetadata%2F48447&protocol=*&session=46faa299c3fb39c8-com-plexapp-android&subtitleSize=100&videoBitrate=200000&videoQuality=100&videoResolution=3840x2160 (12 live) TLS GZIP 44ms 3809 bytes (pipelined: 8)
Dec 19, 2021 16:47:03.024 [0x145f6f9b4b38] DEBUG - Request: [10.19.64.64:44398 (Subnet)] GET /video/:/transcode/universal/start.m3u8?audioBoost=100&autoAdjustQuality=0&directPlay=0&directStream=1&directStreamAudio=1&fastSeek=1&hasMDE=1&location=lan&maxVideoBitrate=200000&mediaBufferSize=209664&mediaIndex=0&partIndex=0&path=%2Flibrary%2Fmetadata%2F48447&protocol=hls&session=46faa299c3fb39c8-com-plexapp-android&subtitleSize=100&videoBitrate=200000&videoQuality=100&videoResolution=3840x2160 (13 live) TLS Signed-in Token (Mothy_Tim) (range: bytes=0-)
Dec 19, 2021 16:47:03.024 [0x145f6f9b4b38] DEBUG - [Transcode] Found session GUID of 46faa299c3fb39c8-com-plexapp-android in session start.
Dec 19, 2021 16:47:03.026 [0x145f6f9b4b38] DEBUG - [Transcode] TranscodeUniversalRequest: using augmented profile Android
Dec 19, 2021 16:47:03.026 [0x145f6f9b4b38] DEBUG - [Transcode] Downloading document http://127.0.0.1:32400/library/metadata/48447?checkFiles=1&includeBandwidths=1&offset=-1&X-Plex-Incomplete-Segments=1&X-Plex-Session-Identifier=46faa299c3fb39c8-com-plexapp-android
Dec 19, 2021 16:47:03.028 [0x145f6f9b4b38] DEBUG - [Transcode] It took 0.000000 ms to retrieve 120 items.
Dec 19, 2021 16:47:03.031 [0x145f6f9b4b38] DEBUG - [Transcode] It took 0.000000 ms to retrieve 120 items.
Dec 19, 2021 16:47:03.082 [0x145f6f9b4b38] DEBUG - [Transcode] We're going to try to auto-select an audio stream for account 1.
Dec 19, 2021 16:47:03.082 [0x145f6f9b4b38] DEBUG - [Transcode] Selecting best audio stream for part ID 54427 (autoselect: 1 language: en)
Dec 19, 2021 16:47:03.082 [0x145f6f9b4b38] DEBUG - [Transcode] We're going to try to auto-select a subtitle.
Dec 19, 2021 16:47:03.082 [0x145f6f9b4b38] DEBUG - [Transcode] Audio Stream: 117182, Subtitle Stream: -1
Dec 19, 2021 16:47:03.083 [0x145f6f9b4b38] DEBUG - [Transcode] Found session GUID of 46faa299c3fb39c8-com-plexapp-android in session start.
Dec 19, 2021 16:47:03.083 [0x145f6f9b4b38] DEBUG - [Transcode] Using session GUID 46faa299c3fb39c8-com-plexapp-android for new transcode session.
Dec 19, 2021 16:47:03.083 [0x145f6f9b4b38] DEBUG - [Transcode] Cleaning directory for session 46faa299c3fb39c8-com-plexapp-android ()
Dec 19, 2021 16:47:03.084 [0x145f74c14b38] DEBUG - Completed: [10.19.64.64:44398] 206 GET /video/:/transcode/universal/start.m3u8?audioBoost=100&autoAdjustQuality=0&directPlay=0&directStream=1&directStreamAudio=1&fastSeek=1&hasMDE=1&location=lan&maxVideoBitrate=200000&mediaBufferSize=209664&mediaIndex=0&partIndex=0&path=%2Flibrary%2Fmetadata%2F48447&protocol=hls&session=46faa299c3fb39c8-com-plexapp-android&subtitleSize=100&videoBitrate=200000&videoQuality=100&videoResolution=3840x2160 (13 live) TLS 59ms 394 bytes (range: bytes=0-)
Dec 19, 2021 16:47:03.194 [0x145f7257cb38] DEBUG - Request: [10.19.64.64:44400 (Subnet)] GET /video/:/transcode/universal/session/46faa299c3fb39c8-com-plexapp-android/base/index.m3u8 (14 live) TLS Signed-in
Dec 19, 2021 16:47:03.194 [0x145f7257cb38] DEBUG - [Transcode/46faa299c3fb39c8-com-plexapp-android] Starting a transcode session 46faa299c3fb39c8-com-plexapp-android at offset -1.0 (state=3)
Dec 19, 2021 16:47:03.195 [0x145f7257cb38] DEBUG - [Transcode/46faa299c3fb39c8-com-plexapp-android] TPU: hardware transcoding: enabled, but no hardware decode accelerator found
Dec 19, 2021 16:47:03.195 [0x145f7257cb38] DEBUG - [Transcode/46faa299c3fb39c8-com-plexapp-android] [Universal] Using local file path instead of URL: /data/Movies/Gremlins 2 The New Batch (1990)/Gremlins.2.The.New.Batch.1990.Unknown.mkv
Dec 19, 2021 16:47:03.195 [0x145f7257cb38] DEBUG - [Transcode/46faa299c3fb39c8-com-plexapp-android] TPU: hardware transcoding: final decoder: , final encoder:
Dec 19, 2021 16:47:03.195 [0x145f7257cb38] DEBUG - [Transcode/46faa299c3fb39c8-com-plexapp-android/JobRunner] Job running: FFMPEG_EXTERNAL_LIBS='/config/Library/Application\ Support/Plex\ Media\ Server/Codecs/fb9eae3-4185-linux-x86_64/' X_PLEX_TOKEN='xxxxxxxxxxxxxxxxxxxx' '/usr/lib/plexmediaserver/Plex Transcoder' '-codec:0' 'h264' '-noaccurate_seek' '-analyzeduration' '20000000' '-probesize' '20000000' '-i' '/data/Movies/Gremlins 2 The New Batch (1990)/Gremlins.2.The.New.Batch.1990.Unknown.mkv' '-map' '0:0' '-metadata:s:0' 'language=eng' '-codec:0' 'copy' '-map' '0:1' '-metadata:s:1' 'language=eng' '-codec:1' 'copy' '-segment_format' 'matroska' '-f' 'ssegment' '-individual_header_trailer' '0' '-flags' '+global_header' '-segment_header_filename' 'header' '-segment_time' '10' '-segment_start_number' '0' '-segment_copyts' '1' '-segment_time_delta' '0.0625' '-segment_list' 'http://127.0.0.1:32400/video/:/transcode/session/46faa299c3fb39c8-com-plexapp-android/5f833f3a-996a-45cb-a9a0-4f043cf2145c/manifest?X-Plex-Http-Pipeline=infinite' '-segment_list_type' 'csv' '-segment_list_size' '5' '-segment_list_separate_stream_times' '1' '-segment_list_unfinished' '1' '-segment_format_options' 'output_ts_offset=10' '-max_delay' '5000000' '-avoid_negative_ts' 'disabled' '-map_metadata:g' '-1' '-map_metadata:c' '-1' '-map_chapters' '-1' 'media-%05d.ts' '-start_at_zero' '-copyts' '-vsync' 'cfr' '-y' '-nostats' '-loglevel' 'quiet' '-loglevel_plex' 'error' '-progressurl' 'http://127.0.0.1:32400/video/:/transcode/session/46faa299c3fb39c8-com-plexapp-android/5f833f3a-996a-45cb-a9a0-4f043cf2145c/progress'
Dec 19, 2021 16:47:03.196 [0x145f7257cb38] DEBUG - [Transcode/46faa299c3fb39c8-com-plexapp-android/JobRunner] Jobs: Starting child process with pid 840