Severe lag using Media track in 4.27 Sequencer

This can be done with empty UE project. When you have a media track inside your sequencer and you play it, there’s about 50/50 chance for it to freeze the entire engine for a good 10 seconds, printing out the error:

LogMediaUtils: Error: Blocking media playback timed out. Disabling it for this playback session.

This happens both in editor and PIE. Digging into the code I seems to found that somehow the MediaPlayerFacade, using the playbackSettingV2, failed to retrieve the latest video sample, causing it to loop indefinitely until the BlockOnTime timer ran out. The initial 10 second lag can be resolved via SetBlockOnTimeRange to 0, but it doesn’t seem to remedy the subsequent low video framerate, almost 1~3 frames per second.