Fire TV: Plex does not play anything anymore

Example:

  1. Plex XML
<Media id="210745" duration="8459456" bitrate="28924" width="1920" height="1080" aspectRatio="1.78" audioChannels="8" audioCodec="truehd" videoCodec="h264" videoResolution="1080" container="mkv" videoFrameRate="24p" videoProfile="high">
<Part accessible="1" exists="1" id="210917" key="/library/parts/210917/1584311419/file.mkv" duration="8459456" file="/share/movies/Fantastic Beasts The Crimes of Grindelwald (2018)/Fantastic Beasts The Crimes of Grindelwald (2018).mkv" size="30585366229" container="mkv" videoProfile="high">
<Stream id="167921" streamType="1" default="1" codec="h264" index="0" bitrate="28476" language="English" languageCode="eng" bitDepth="8" chromaLocation="left" chromaSubsampling="4:2:0" codedHeight="1088" codedWidth="1920" frameRate="23.976" hasScalingMatrix="0" height="1080" level="41" profile="high" refFrames="2" scanType="progressive" width="1920" displayTitle="1080p (H.264)"/>
<Stream id="167922" streamType="2" selected="1" default="1" codec="truehd" index="1" channels="8" language="English" languageCode="eng" audioChannelLayout="7.1" bitDepth="24" samplingRate="48000" title="TrueHD Atmos 7.1" displayTitle="English (TRUEHD 7.1)"/>
<Stream id="167923" streamType="2" codec="ac3" index="2" channels="6" bitrate="448" language="English" languageCode="eng" audioChannelLayout="5.1(side)" samplingRate="48000" title="AC3 5.1-EX" displayTitle="English (AC3 5.1)"/>
<Stream id="167924" streamType="3" codec="pgs" index="3" language="English" languageCode="eng" headerCompression="1" title="English (SDH)" displayTitle="English (PGS)"/>
</Part>
</Media>
  1. ffmpeg
Input #0, matroska,webm, from 'Fantastic Beasts The Crimes of Grindelwald (2018).mkv':
  Metadata:
    title           : Fantastic Beasts: The Crimes of Grindelwald
    encoder         : libebml v1.3.10 + libmatroska v1.5.2
    creation_time   : 2020-03-15T22:29:00.000000Z
  Duration: 02:20:59.46, start: 0.000000, bitrate: 28924 kb/s
  1. mediainfo
Complete name                            : Fantastic Beasts The Crimes of Grindelwald (2018).mkv
Format                                   : Matroska
Format version                           : Version 4
File size                                : 28.5 GiB
Duration                                 : 2 h 20 min
Overall bit rate mode                    : Variable
Overall bit rate                         : 28.9 Mb/s
Movie name                               : Fantastic Beasts: The Crimes of Grindelwald
Encoded date                             : UTC 2020-03-15 22:29:00
Writing application                      : mkvmerge v44.0.0 ('Domino') 64-bit
Writing library                          : libebml v1.3.10 + libmatroska v1.5.2

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L4.1
Format settings                          : CABAC / 2 Ref Frames
Format settings, CABAC                   : Yes
Format settings, ReFrames                : 2 frames
Codec ID                                 : V_MPEG4/ISO/AVC
Duration                                 : 2 h 20 min
Bit rate mode                            : Variable
Width                                    : 1 920 pixels
Height                                   : 1 080 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 23.976 (24000/1001) FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Language                                 : English
Default                                  : Yes
Forced                                   : No

Audio #1
ID                                       : 2
Format                                   : MLP FBA 16-ch
Format/Info                              : Meridian Lossless Packing FBA with 16-channel presentation
Commercial name                          : Dolby TrueHD with Dolby Atmos
Codec ID                                 : A_TRUEHD
Duration                                 : 2 h 20 min
Bit rate mode                            : Variable
Maximum bit rate                         : 4 953 kb/s
Channel(s)                               : 8 channels
Channel layout                           : L R C LFE Ls Rs Lb Rb
Sampling rate                            : 48.0 kHz
Frame rate                               : 1 200.000 FPS (40 SPF)
Compression mode                         : Lossless
Title                                    : TrueHD Atmos 7.1
Language                                 : English
Default                                  : Yes
Forced                                   : No
Number of dynamic objects                : 15
Bed channel count                        : 1 channel
Bed channel configuration                : LFE

Audio #2
ID                                       : 3
Format                                   : AC-3
Format/Info                              : Audio Coding 3
Commercial name                          : Dolby Digital
Codec ID                                 : A_AC3
Duration                                 : 2 h 20 min
Bit rate mode                            : Constant
Bit rate                                 : 448 kb/s
Channel(s)                               : 6 channels
Channel layout                           : L R C LFE Ls Rs
Sampling rate                            : 48.0 kHz
Frame rate                               : 31.250 FPS (1536 SPF)
Bit depth                                : 16 bits
Compression mode                         : Lossy
Stream size                              : 452 MiB (2%)
Title                                    : AC3 5.1-EX
Language                                 : English
Service kind                             : Complete Main
Default                                  : No
Forced                                   : No

Text
ID                                       : 4
Format                                   : PGS
Muxing mode                              : zlib
Codec ID                                 : S_HDMV/PGS
Codec ID/Info                            : Picture based subtitle format used on BDs/HD-DVDs
Title                                    : English (SDH)
Language                                 : English
Default                                  : No
Forced                                   : No

All 3 match.