Wireless clients cannot communicate if connected to different APs

Hello

I have some APs connected to my SG230. The Wi-Fi network is configured as "Bridge to AP lan". It happens a strange behaviour:

- If client A and client B are connected to the same access point, they can communicate each other, they are pingable.

- If client A and client B are connected to different access points, they cannot communicate, they are no ping visible.

- If client C is connected to wired connection, it can ping both client A and client B.

The issue is not dependent on AP model...

any ideas?

Thanks!