Create four canonical fandom tags. I'll call them Fandom A, Fandom B, Fandom C, and Fandom D.
Edit Fandom A and add subtags Fandom B and Fandom C.
Edit Fandom D and add metatags Fandom B and Fandom C.
Edit Fandom C and remove Fandom A from its metatags.
Keep refreshing the edit page until Fandom A disappears, then remove Fandom D from its subtags.
Post a work with Fandom D.
Go to the works page for Fandom D and wait for the work to appear.
In the "Other tags to include" field of the filters, enter "Fandom A" and press "Sort and Filter."
The work does not appear.
Note that if you instead entered “Fandom B” in the field, the work would appear. This is because Fandom D has Fandom B as a direct metatag, but it is missing the inherited metatag Fandom A.
You can also test this by checking the work listings for Fandom A and Fandom B. The work with Fandom D will appear on the page for Fandom B, but not on the page for Fandom A.
The work should appear. Fandom D should have Fandom A as an inherited metatag.
This often happens alongside AO3-5507 in production, as seen in Marvel fandoms. The issues can, however, occur separately. (According to ticking, there are over 40,000 works in the "Marvel Cinematic Universe" tag that are missing the "Marvel" metatag, and this bug counts for about 13,000 of those.)
This is not super high priority as we are eyeing a rewrite of this code. However, it's good to have these things logged.
This issue was responsible for AO3-5484 .