Added as issue https://github.com/openstreetmap/iD/issues/3929

Ah, I think I know what the issue is. I've noticed if the wikipedia field was present for an item without selecting the dropdown and you edit the wikidata field is not queried and added. Actually there is a broader issue with this issue too, at least there was from what I observed in my last wikipedia linking sprint. Items which already have a wikipedia entry do not also have a wikidata entry and to correct one must delete the wikipedia field then add again for the wikidata field to be automatically added. Might be worth verifying and reporting that or looking into why that is occurring since it does cause a data completeness issues like this missing the wikidata entry.

Yes, I'm using the dropdown wikipedia field to get the wikidata association as well.