I'm facing this same issue. I was able to load and watch the videos by re-encoding them to the VP9 format. The original video format was WebM and encoded with HEVC (I'm not entirely sure if it was HEVC and WebM. I will check again when I turn on my laptop).
Also my friends couldnt load and watch the video in their side as well.
This is good information, thanks! What's your build info? You can find it by opening User Settings > pressing on the build info at the bottom-left.
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Comment by Hampus