Yeah, as above, most thumbnailing logic is now in Discourse. I actually override to loosen the inclusion requirement slightly, but it still may be stricter than before.
I’m wary of overriding any more and really the ‘looseness’ of the criteria for considering something worthy of thumbnailing should now be a core issue. TLP should really just be a customer of that data.
OK now picked up here: Problems with thumbnails from Soundcloud and YouTube oneboxes