Jellyfin media won't play with hardware transcoding

[riqsha]

Basically title. I had hardware transcoding enabled for a few days now. My partner generally accesses jellyfin directly from the IP address on firefox on windows whereas I have the nameserver for my local dns (blocky) set up on my laptop (lenovo legion pro 7i 16irx8h running nixos 25.11.20250928.e9f00bd (Xantusia)) and access jellyfin on a domain (this is reverse proxied on caddy). 

Last evening jellyfin videos just refused to play for her. She claims it's because she tried to enable subtitles on a new video she'd downloaded. At the time, files continued to play for me while accessing them both on the jellyfin app and the browser. But if I accessed the same files via the IP address they would play fine. This started working again when I disabled hardware transcoding. All of last night these errors were only via the IP address. 

As of this morning while I was retesting these to create this post the videos don't play on the domain name version either - notably tho I'm currently connected to my 34 inch ultrawide monitor. One anime file was playing and I've attached logs for that as well.

Server details:

i5 9500t 
nixos 25.11.20250928.e9f00bd (Xantusia)
jellyfin runs via systemd using the nixos service

Jellyfin hw transcoding setup:

QSV
All hw decoding enabled except AV1
Prefer OS native DXVA or VA-API hardware decoders - true
Enable hardware decoding - true
Allow encoding in HEVC format - true
Enable VPP Tone mapping - true
Allow subtitle extraction on the fly - true

Jellyfin log from this morning
ffmpeg log of a file that refused to work
ffmpeg log of a file that worked even with hw transcode enabled

[schnappi]

I know this isn't the answer you want, but is she willing to try playing through the Jellyfin Media Player? Even if not, can you temporarily (before removing, including all registry and app data) install for and test to see if the issue occurs when playing through the Jellyfin Media Player?