I have RADIUS from Windows 2016. It works fine until 4 days. I see error 22 in Event, security, problem with EAP. Finally, I configured the 20 AP with WPA2 without RADIUS, pre-shared key.
The AP are AIR-AP1131AG-E-K9, firmware version 12.3(8)JA2, 10 o more years old.
Is it compatible RADIUS from Windows 2016 with that model o firmware?
The AP will work with that RADIUS server.
As it stopped working 4 days ago, check the certificate on the RADIUS server.
Ensure that the AP or WLC (dependent on if LWAP or autonomous mode) is added as a network device to RADIUS.
You should be able to look at the RADIUS logs to understand why its failing and search the error codes given in the NPS forums