Issue

When syncing user segments in Segment Engage to a downstream destination, you may experience an audience size mismatch where your destination platform contains a significantly larger audience count than Segment. This issue commonly occurs after deleting an audience in Segment and subsequently creating a brand-new audience using the exact same audience key.

Product

Segment

Environment

Segment Console

Cause

When you delete an audience from your Segment workspace, the historical membership data is not automatically deleted from your downstream tools, nor is it deleted from your resolved user profiles. Instead, the audience key and its true/false values remain permanently attached to those profiles in Unify, converting into a custom trait.

If you create a new audience using that exact same audience key, downstream destinations cannot distinguish between the old, deleted audience and the new one. Because they share the same key, the destination will aggregate the members of the old audience with the new one, leading to severely inflated audience counts and incorrect customer targeting downstream.

Resolution

To fix an audience size mismatch caused by a reused key, you must delete the affected audience and recreate it using a completely unique key:

Step 1: Delete the Audience with the Reused Key

1. In the Segment Console, navigate to Engage > Audiences.
2. Click on the audience that is currently experiencing the size mismatch.
3. Click the Settings tab.
4. Under the settings menu, toggle the status from Enabled to Disabled.
5. Click Delete Audience and confirm by clicking Delete Audience in the prompt

Step 2: Recreate the Audience with a Unique Key

1. Go back to your Audiences list view.
2. Click New Audience to build the segment from scratch, or click the More Options (three dots) icon next to your previously deleted audience and select Clone to copy the exact audience builder rules into a new draft.
3. Reconfigure your audience rules, preview the results, and proceed to the Review & Create page.
4. In the Audience Key field, input a completely unique key that has never been used in your workspace before. Do not reuse the old key.
5. Connect your downstream destination, review, and click Create Audience. Segment will begin a clean, accurate backfill to your destination.

Additional Information 

You cannot edit or change an audience key once the audience is saved. While Segment allows you to change the display name of an audience, doing so will not update the audience name or key in downstream ad platforms (such as Facebook or Google Ads). If you need to change how the audience is referenced downstream, you must always re-create the audience with a brand-new key.

As a best practice, if you are targeting ad platforms, make sure to manually delete the old, retired audience directly within the downstream ad network dashboard to prevent residual data from affecting your campaigns.