Our process for adding subtags happens in two places: once in the backend to store the hash and metadata, and once in the presentation layer to attach to the link.

There was a bug in our logic that was saving the incorrect subtag, if the backend and presentation layer subtags didn’t match. This most often happened in situations where javascript wasn’t running - namely in AMP.

We’ve since updated our logic to ensure that subtags match on both the backend and the presentation layer.