No ASS Subtitles (MKV Video) in Roku Jellyfin Client

I'm experiencing an issue with ASS subtitles not displaying on the Roku Jellyfin client (using any/all known client/server settings).

“Custom Subtitles” (with fallback font) seemed the most promising solution, but also no luck there. [Note: When using Jellyfin web client, subtitles do appear with the fallback font.]

I've also seen this reported in GitHub Issue #687: "mkv with single ASS subtitle track (forced English) will not show subtitles."

My setup:

· Jellyfin Server: 10.11.11-a running on QNAP ARM64 (installed via QPKG)
· Jellyfin Client: Roku client version 3.2.3
· Roku Device: 3840R - Streaming Stick
· Media file: MKV container with internal ASS/SSA subtitle track

What I've tried:

1. Installed a fallback font on the server (OTF format [CourierPrime-Regular.otf], under 5 MB [142KB]).
2. Verified the font works by playing the same video in the Jellyfin web browser client → subtitles displayed correctly, confirming the font file is valid and the server can render ASS subtitles.
3. Enabled "Custom Subtitles" in the Roku client settings.
4. Toggled the following Roku client settings one at a time with no change:
· "Burn subtitles" (Auto / Always / Disabled)
· "Text subtitles only" (On / Off)
· "Custom subtitles" (On / Off)
5. Confirmed Roku system-wide caption settings are set to "Off”.

Result:
ASS subtitles still do not display on the Roku Jellyfin client. The video plays fine, but no subtitles appear.

General Note:
All of the above is using direct play (i.e., no transcoding).

Any assistance would be greatly appreciated. Thanks in advance!