Hi Anrich,
The issue you describe seems to indicate a mis-configuration issue.
As part of the Wi-Fi standard a client device should seamlessly roam from AP-to-AP, providing they have identical WLAN configuration and overlapping coverage.
Even if the APs do not have overlapping coverage, the client device should automatically associate to the SSID; providing it has an identical configuration.
If your clients are prompting for re-authentication then it could be that the WLAN configuration on AP-X differs to that on the AP-Y the client is trying to roam to.
Thanks,
Darrel.