Subtitle Issue - unknown format error

I have some TV shows I’m watching and the media files (x265 format) play fine. When I turn on subtitles and go to play again I get an “unrecognized format” error for the media. When I play the same files on my computer with VLC there are no issues or errors.
Any suggestions on how to turn subtitles on without Plex thinking the file is corrupt?

Would you mind sharing what kind of subtitles we’re talking about?
FWIW this could easily be some strange/exotic format that VLC happens to support but Plex has never heard of.

Ideally provide the related snipped of subtitle information from > Get Info > Show XML

Built in subtitles - I did not add an SRT file.
VLC tells me “Substation Alpha subtitles (ssa)” whatever that means?

Sorry - just saw the last line of your response. See “show XML” below. I ended up downloading a different subtitle SRT as a work around but curious if I could have got the built in subtitles to work!

<MediaContainer size="1" allowSync="1" identifier="com.plexapp.plugins.library" librarySectionID="4" librarySectionTitle="TV Shows" librarySectionUUID="a27110a1-bdbc-49e3-a5c6-3f82259f4e70" mediaTagPrefix="/system/bundle/media/flags/" mediaTagVersion="1634921915">

<Video ratingKey="4135" key="/library/metadata/4135" parentRatingKey="4132" grandparentRatingKey="4131" guid="plex://episode/61634b3d96699883d0cc9f11" parentGuid="plex://season/6162f6c5d70a9adffbffbcd0" grandparentGuid="plex://show/5d9c082308fddd001f29344e" type="episode" title="Nadiya" grandparentKey="/library/metadata/4131" parentKey="/library/metadata/4132" librarySectionTitle="TV Shows" librarySectionID="4" librarySectionKey="/library/sections/4" grandparentTitle="Hanna" parentTitle="Season 3" contentRating="TV-MA" summary="Hanna and Marissa move quickly now that they’ve been exposed. They plan to head to Vienna, believing it’s the headquarters of Pioneer and home of the assassination program but Hanna first goes in search of Abbas. Marissa continues on to Vienna. Both are unaware they are heading into a trap." index="3" parentIndex="3" audienceRating="8.0" viewCount="2" skipCount="1" lastViewedAt="1638315307" parentYear="2021" thumb="/library/metadata/4135/thumb/1638185438" art="/library/metadata/4131/art/1637732419" parentThumb="/library/metadata/4132/thumb/1638084211" grandparentThumb="/library/metadata/4131/thumb/1637732419" grandparentArt="/library/metadata/4131/art/1637732419" grandparentTheme="/library/metadata/4131/theme/1637732419" duration="2745600" originallyAvailableAt="1900-01-01" addedAt="1637732409" updatedAt="1638185438" audienceRatingImage="themoviedb://image.rating">

<Media id="4071" duration="2745600" bitrate="1243" width="1920" height="1080" aspectRatio="1.78" audioChannels="6" audioCodec="eac3" videoCodec="hevc" videoResolution="1080" container="mkv" videoFrameRate="24p" videoProfile="main 10">

<Part accessible="1" exists="1" id="4255" key="/library/parts/4255/1638178618/file.mkv" duration="2745600" file="/volume1/Plex/TV Shows/Hanna/Season 3/Hanna.S03E03.1080p.HEVC.x265-MeGusta.mkv" size="427533752" container="mkv" deepAnalysisVersion="6" requiredBandwidths="5131,2721,1503,1344,1344,1344,1344,1344" videoProfile="main 10">

<Stream id="11599" streamType="1" default="1" codec="hevc" index="0" bitrate="603" bitDepth="10" chromaLocation="left" chromaSubsampling="4:2:0" codedHeight="1088" codedWidth="1920" colorPrimaries="bt709" colorRange="tv" colorSpace="bt709" colorTrc="bt709" frameRate="23.976" height="1080" level="120" profile="main 10" refFrames="1" requiredBandwidths="4489,2081,862,706,706,706,706,706" scanType="progressive" width="1920" displayTitle="1080p (HEVC Main 10)" extendedDisplayTitle="1080p (HEVC Main 10)"> </Stream>

<Stream id="11600" streamType="2" selected="1" default="1" codec="eac3" index="1" channels="6" bitrate="640" language="English" languageTag="en" languageCode="eng" audioChannelLayout="5.1(side)" requiredBandwidths="639,639,639,639,639,639,639,639" samplingRate="48000" displayTitle="English (EAC3 5.1)" extendedDisplayTitle="English (EAC3 5.1)"> </Stream>

<Stream id="11601" streamType="3" default="1" forced="1" codec="ass" index="2" bitrate="0" language="English" languageTag="en" languageCode="eng" requiredBandwidths="1,1,1,1,1,1,1,1" title="English [Forced]" displayTitle="English Forced (ASS)" extendedDisplayTitle="English [Forced] (ASS)"> </Stream>

Mod-Edit: added code tags for better readability

From what I’ve seen here, ASS subtitles can be tricky. They might work with some clients but not all – even some of the ones with basic support might not be able to reproduce the subtitles as specified in the ASS file/track