We added unique identifiers for these to bypass mastodon's "feature" of ignoring follow activities for 6 hours after receiving an unfollow activity that doesn't match a known follow relationship (which is not uncommon when debugging federation issues). This causes implementations that expect follow & unfollow to have the same identifier to not be able to reconcile the two. We can't solve this problem for existing follow relationships, but we can add a new column (e.g. activityId, relationshipId or discriminator) that contains a unique identifier for (new) outgoing follows, and use that (with a fallback to the current random identifier) when rendering unfollow activities.