I don't see anything that looks obviously wrong. The channel is opened and you can see ffmpeg parsing content. Two audio streams are found; one is mpeg2audio which I'd guess is stereo, and one is ac3 which I'd guess has 5.1 audio, which is selected alongside the H264 video content.
Disabling VAAPI changes the process flow inside Kodi, although I'd have to go look at code to understand more. I'm wondering what differences might exist/show in the logs as a first step. Please share some additional debug logs (separate logs/pastes if possible, as these are easier to search).
- Show an SD channel with VAAPI disabled
- Show an HD channel being opened
NB: LE did bump the Tvheadend version last week https://github.com/LibreELEC/LibreELEC.tv/pull/10719 but the list of changes in the update are not particularly interesting (compile fixes, translation updates, etc.). There are also ffmpeg changes to improve the transcoding capabilities (mentions of VAAPI here, but this is encoding not decoding) so I'm not immediately seeing a connection to the problem reported.