Comment 7 for bug 1845396

Videos on YouTube work to a certain degree, some videos just start and cannot seek, and some don't play at all. However, playing videos (all websites) in Epiphany has not been the greatest experience even before this update. So I don't think this is actually a regression.

Actually the upstream changelog mentions that videos on YouTube are not 100% reliable:
3.28.5 - September 21, 2018
===========================

This release is intended to fix video playback on YouTube. We believe that
YouTube began requiring media source extensions to play WebM videos on Tuesday
of this week, so we have enabled it.

You are strongly encouraged to update to WebKitGTK+ 2.22.2 and the forthcoming
GStreamer 1.14.4 to minimize video playback disruptions. It's not really
reliable enough to be enabled yet, but it's a whole lot better than no YouTube.