Seems reasonable to go straight to default, since it should only affect the 12 wikis where sub-referencing is currently deployed.

I would recommend possible next steps if we need better information:

• Add logic to the dump scraper to search for "*.pdf" links within ref tags and sum how often PDF links are present in refs, per wiki.
• Take a random sample of 100 PDF links from the logs, and run them through the production Citoid service using a script, then review what kind of success rate and resulting metadata we're seeing.

From https://logstash.wikimedia.org/goto/2b68a9fe1a121202c3d11af766145984 , looking at Citoid requests matching "pdf" over the past 90 days:

Remaining work should happen on top of T425776: Add 'Jump to reference list' link to Reference Preview popup, once that patch is complete.

Note that the patch is a workaround because it's still possible to reintroduce the issue. I would suggest taking further measures such as introducing a new hook, or documenting that extensions should / should not rely on onBeforeInitialize to set up TestKitchen experiments...

Please don't delete referencepreviewspopups in this round! We still need the data, although we might be able to clean older history once we figure out exactly what is still relevant.

I still don't have exact steps to reproduce, the behavior flaps back and forth on my browser and I'm not sure which steps are causing the effect and which are irrelevant... All I can say so far is that it only happens in Firefox "Responsive Design Mode".