I can still hear the audio, and it should be playing the video, but the preview screen is blank with the default checkered background.
I have ran into this issue a few times. What happened to me was the the "link" icon was not clicked in the speed/duration dialogue box. If it is clicked, it should be blue. If it is not clicked, it will show the symbol split with a line going through. If you change the speed percentage, the video duration must be linked to change too and vice versa. Hope this works for you!
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