This has been an issue for a while but I first noticed it on my Nvidia Shield TV Pro 2017 that when I adjust the Playback Speed on recordings from HDHomeRun, it only appears to affect the video. The audio runs at 1x no matter what speed I pick causing it to go out of sync immediately. Things recorded from other sources like TV Everywhere or Pluto play at the right speed when set.
Could it be something to do with the MPEG2 source of the HDHomerun recordings? When I adjust playback speed on the same recordings via Channels on my Pixel 7 Pro, it runs at the appropriate speed. So it appears to be something with the Shield specifically. Happy to provide whatever logs that may help. Also had this issue on a Shield TV Pro 2019. Both Sheids are fully updated, system and app.