When I have the Uno interface enabled in Plex Web (via Settings>General>Preview the new Plex experience) the edit pop-up window for any video collection only shows the infinitely spinning wheel. No metadata fields ever display.
With the Settings>General>Preview the new Plex experience option disabled, the edit pop-up window for video collections works just fine.
Known issue…? I did some searching on the forum before posting this, but could not find any mention of it.