Sorry, it's not clear: is your HPE A5500 SI Switch software version at A5500SI-CMW520-R2221P12 (which isn't the latest one since it was released during the second quarter of 2015) or what?
The latest software release (Posted on May, 27th 2016) for the JD369A HPE 5500-24G SI Switch is the A5500SI-CMW520-R2221P22 and, reading its Release Notes, there are some refrences to fixes regarding RADIUS/Authentication Servers.
It should worth a try if you haven't yet upgraded your Switch to that release.