Epiphany browser video playback showing slideshow (maybe keyframes) not video

Reproduction:

1. Go to https://puri.sm/posts/mobile-desktop-convergence/
2. In Epiphany/Web as well as Chromium
3. Push play on the video
4. Watch Epiphany/Web slideshow the video with smooth audio
5. Watch Chromium play smooth audio and video

purism-librem-5-pureos-epiphany-video-playback-2020-11-29

purism@pureos:~$ uname -a
Linux pureos 5.9.0-1-librem5 #1 SMP PREEMPT Fri Nov 27 19:15:53 UTC 2020 aarch64 GNU/Linux
purism@pureos:~$ dpkg -s phosh | grep Version
Version: 0.6.0
purism@pureos:~$ dpkg -s phoc | grep Version
Version: 0.5.1
purism@pureos:~$ dpkg -s epiphany-browser | grep Version
Version: 3.38.1-1pureos3
purism@pureos:~$ dpkg -s chromium | grep Version
Version: 83.0.4103.116-1~deb10u3
purism@pureos:~$