SOLVED: Video freezing on TV App

[f-d-ffm]

Are the browsers remuxing?  Or is only the Android TV remuxing?

As I can see, both of them are remuxing. But I'm not quite sure. I get this message on the jellyfin dashboard, when clicking on the "i" button on the currently playing media (see attachment). It says (translated) :

REMUXING
The media is in an incompatible file container (MKV, AVI, WMV), but video as well as audio are compatible with the device. The media will be repacked during playback, before they get sent to the device. The Remux needs very little compute power, with original media quality.

This message is the same for playback on the TV Box as well as on a browser.
All my files are either in the mp4 or MKV container. All of them are h.265 files with stereo aac sound (multiple languanges) and subtitle tracks. They all still worked before my vacation, no problem.

Can I change the remux settings per device? I only found the settings for Remux within the user settings.

Do you need more information? What else can I provide?

Thanks in advance.