C5x 2.5.3 firmware

Morning,

We are experiencing issues downgrading a new batch of C5x’s we’ve received from version 2.5.3 to 2.5.2.1 in order to connect to our A5c access points. This a bit of an issue as we have a few A5’s in the field and there is no 2.5.3 firmware upgrade available? Any advice?

Regards,