We are using Topic List Previews with tiles in our main page. Yesterday we had to rebuild our instance for reasons unrelated to TPL. We were aware of the change of thumbnailing backend in Discourse core and we knew that upgrading could cause problems with thumbnails. Still, it had to be done.
Anyway, after rebuilding (including the Postgres upgrade), all thumbnails coming from oneboxes were gone. No problem, we rebaked all posts and then most thumbnails reappeared (good) but not all (intriguing and bad). We rebaked a couple more times just in case, but there are some remaining posts that won’t get their thumbnail in the main page even if the oneboxes render without problems in their topic page.
Two patterns detected so far:
- Soundcloud oneboxes render without problems, but the thumbnail is missing systematically ("Select Thumbnail will show no thumbnails), and no rebuild HTML will solve this. For instance, check Female:pressure podcast episode 60 Inverno - female:pressure podcast - EQlzr.
- Some thumbnails of YouTube oneboxes were missing in the main page (only some) and then, after visiting the topic page, they would magically appear in the main page. However…
There is one (and only one, the last one) topic with a YouTube onebox that won’t generate a thumbnail, no idea why: Look Mom No Computer (DIY Synths) - Listen / Watch - EQlzr.