Sometimes the device memory becomes fragmented or corrupted, especially if you frequently upload/download user data.

If you have tried all the above and still face "Authentication Failure," the hardware may be failing. Contact support if:

Outdated firmware is a primary cause of algorithm mismatch. ZKTeco updates its matching algorithms periodically.

Face devices (like ZKTeco SpeedFace) fail in poor lighting or direct sunlight.

This is a sneaky cause of failure that often gets overlooked. If the internal clock on your ZKTeco device is wrong, authentication can fail.

If your device supports duress fingers (a finger that silently alarms), ensure you haven't accidentally used that specific finger for regular access. If the duress finger is scanned, the device may show "Authentication Failure" to avoid alerting the intruder while sending a silent alarm.