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I just discovered why some of my followers from larger #Mastodon instances (like mastodon.social) would mysteriously unfollow me after a while!

A pull request was just merged in Mastodon that fixes a critical bug in their follower synchronization mechanism.

Turns out Mastodon implements the FEP-8fcf specification (Followers collection synchronization across servers), but it expected all followers to be in a single page collection. When followers were split across multiple pages, it would only see the first page and incorrectly remove all followers from subsequent pages!

This explains so much about the strange behavior I've been seeing with #Hollo and other #Fedify-based servers over the past few months. Some people would follow me from large instances, then mysteriously unfollow later without any action on their part.

Thankfully this fix has been marked for backporting, so it should appear in an upcoming patch release rather than waiting for the next major version. Great news for all of us building on #ActivityPub!

This is why I love open source—we can identify, understand, and fix these kinds of interoperability issues together.