Play the video here: https://developer.apple.com/videos/play/wwdc2021/10033/ Then seek the video. Audio playback will work properly, but the image will freeze where it was before the seek.
I suspect this is a GStreamer bug.
Yet another HLS-related bug. This page can fallback to MSE and then seek works.
HLS is disabled since https://commits.webkit.org/258717@main.