Strange embedded subtitle behaviour

[Ethanator10000]

Certain movies are giving me a lot of trouble with subtitles. 


Video
Title: 4K HEVC Dolby Vision Profile 7.6 (HDR10)
Codec: HEVC
AVC: No
Profile: Main 10
Level: 153
Resolution: 3840x2160
Aspect ratio: 16:9
Anamorphic: No
Interlaced: No
Framerate: 23.976025
Bitrate: 71960 kbps
Bit depth: 10 bit
Video range: HDR
Video range type: DOVIWithEL
DV title: Dolby Vision Profile 7.6 (HDR10)
DV version major: 1
DV version minor: 0
DV profile: 7
DV level: 6
DV rpu preset flag: 1
DV el preset flag: 1
DV bl preset flag: 1
DV bl signal compatibility id: 6
Color space: bt2020nc
Color transfer: smpte2084
Color primaries: bt2020
Pixel format: yuv420p10le
Ref frames: 1

Subtitle
Title: English - SUBRIP
Language: eng
Codec: SUBRIP
AVC: No
Default: No
Forced: No
External: No

Subtitle
Title: SDH - English - Hearing Impaired - SUBRIP
Language: eng
Codec: SUBRIP
AVC: No
Default: No
Forced: No
External: No

Subtitle
Title: SDH / Centered / PGS - English - Hearing Impaired - PGSSUB
Language: eng
Codec: PGSSUB
AVC: No
Resolution: 1920x1080
Default: No
Forced: No
External: No

I can play this movie fine without any subtitles (Direct Stream with audio repackaging) but I get strange behaviour when I enable subtitles.

The English-SUBRIP and SDH SUBRIP options give me the same errors on my server, and subtitles are not displayed. Video playback sometimes fails or constantly freezes too.

[00:57:34] [ERR] [27] Jellyfin.Api.Middleware.ExceptionMiddleware: Error processing request. URL GET /Videos/4b2f9ca7-405a-1d03-6d5a-ccd7d544b705/4b2f9ca7405a1d036d5accd7d544b705/Subtitles/5/0/Stream.subrip.
System.ArgumentException: Unsupported format: srt
  at MediaBrowser.MediaEncoding.Subtitles.SubtitleEditParser.Parse(Stream stream, String fileExtension)
  at MediaBrowser.MediaEncoding.Subtitles.SubtitleEncoder.ConvertSubtitles(Stream stream, String inputFormat, String outputFormat, Int64 startTimeTicks, Int64 endTimeTicks, Boolean preserveOriginalTimestamps, CancellationToken cancellationToken)
  at MediaBrowser.MediaEncoding.Subtitles.SubtitleEncoder.MediaBrowser.Controller.MediaEncoding.ISubtitleEncoder.GetSubtitles(BaseItem item, String mediaSourceId, Int32 subtitleStreamIndex, String outputFormat, Int64 startTimeTicks, Int64 endTimeTicks, Boolean preserveOriginalTimestamps, CancellationToken cancellationToken)
  at Jellyfin.Api.Controllers.SubtitleController.GetSubtitle(Guid routeItemId, String routeMediaSourceId, Int32 routeIndex, String routeFormat, Nullable1 itemId, String mediaSourceId, Nullable1 index, String format, Nullable1 endPositionTicks, Boolean copyTimestamps, Boolean addVttTimeMap, Int64 startPositionTicks)
  at lambda_method10194(Closure, Object)
  at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfActionResultExecutor.Execute(ActionContext actionContext, IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
  at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask1 actionResultValueTask)
  at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
  at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
  at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
  at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync()
--- End of stack trace from previous location ---
  at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|25_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
  at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)
  at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
  at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeFilterPipelineAsync()
--- End of stack trace from previous location ---
  at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
  at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
  at Jellyfin.Api.Middleware.ServerStartupMessageMiddleware.Invoke(HttpContext httpContext, IServerApplicationHost serverApplicationHost, ILocalizationManager localizationManager)
  at Jellyfin.Api.Middleware.WebSocketHandlerMiddleware.Invoke(HttpContext httpContext, IWebSocketManager webSocketManager)
  at Jellyfin.Api.Middleware.IPBasedAccessValidationMiddleware.Invoke(HttpContext httpContext, INetworkManager networkManager)
  at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
  at Jellyfin.Api.Middleware.QueryStringDecodingMiddleware.Invoke(HttpContext httpContext)
  at Swashbuckle.AspNetCore.ReDoc.ReDocMiddleware.Invoke(HttpContext httpContext)
  at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext)
  at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
  at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
  at Jellyfin.Api.Middleware.RobotsRedirectionMiddleware.Invoke(HttpContext httpContext)
  at Jellyfin.Api.Middleware.LegacyEmbyRouteRewriteMiddleware.Invoke(HttpContext httpContext)
  at Microsoft.AspNetCore.ResponseCompression.ResponseCompressionMiddleware.InvokeCore(HttpContext context)
  at Jellyfin.Api.Middleware.ResponseTimeMiddleware.Invoke(HttpContext context, IServerConfigurationManager serverConfigurationManager)
  at Jellyfin.Api.Middleware.ExceptionMiddleware.Invoke(HttpContext context)

The SDH Centered PGSSUB option does work but for some reason causes a (seemingly slow) transcode: "Reason for transcoding The video's range type is not supported". The subtitles are also grey instead of white. I don't get why the range type becomes a problem when the subtitles are enabled. 

I've gotten PGS and SRT to direct play just fine in other videos, and I was able to download external SRTs for this movie which direct stream perfectly like when the subtitles were disabled. I copied the .mkv over to my computer and I can play the movie with the embedded subtitles just fine there. When going into my jellyfin config/data/data/subtitles folder I find that all the .srt files for this movie are empty (I removed the folder to force the creation of a new one that would only be for this movie). Really confused as to what's going on here.