Spike in Visual Authenticity failures on Facial Similarity Motion randomness checks

## Summary

On 24 August 2026, between 15:00 UTC and 06:53 UTC the following morning, Facial Similarity Motion checks using randomness challenges failed at a much higher rate than normal in the EU region. A stricter validation was applied to all customers in the region when it should have been limited to a single customer, causing verifications that would otherwise have passed to be rejected. Affected reports were returned with a "Visual Authenticity" failure.

Because Motion checks are fully automated, the end users behind these reports were rejected with no manual review, and some attempted the check again and were rejected a second time.

The clear rate for these checks fell from around 97% to around 54% for approximately 1.67% of Facial Similarity Motion reports were affected. Disabling the change restored normal clear rates immediately. Other Motion checks and other regions were unaffected.

## Root Causes

A stricter validation of the motion randomness challenge was being trialled with a single customer, controlled by a per-customer configuration setting. A bug in our code meant the setting was evaluated without the customer identifier, so the stricter validation was applied to all customers in the EU region running Motion with randomness checks rather than to the intended one. Verifications that would have passed under the standard validation were rejected instead, and reported under the "Visual Authenticity" breakdown. No customer configuration or submitted data was at fault.

## Timeline

All times UTC.

* 24 August, 15:00: we enabled a stricter validation for motion randomness challenges in the EU region. Motion checks using randomness began failing at a much higher rate.
* 24 August, 16:36: a customer reported a drop in workflow success rates and we began investigating.
* 25 August, 04:18: we confirmed the elevated failure rate and escalated it.
* 25 August, 06:53: we reverted the change and clear rates returned to normal within minutes.
* 26 August: we deployed a permanent fix.

## Remedies

* Strengthen the controls around customer-specific configuration changes to ensure they cannot be applied more broadly than intended.
* Improve monitoring and alerting for Motion randomness clear rate checks so that unexpected changes in rejection rates are detected automatically and escalated more quickly.

Facial Similarity Motion checks using randomness challenges are failing at a much higher rate than normal in the EU region.