WLC 5520 is unreachable in DNA notification email

[smcisco]

I have a Wireless controller with HA mode and I tried to switch over it is working in both modes primary and secondary, but DNA says the WLC controller is not reachable.

I can ping to DNA from Wireless controller to DNA and DNA to Wireless controller and in the discovery says it is reachable and it was working since last year but recently receiving notification from DNA that WLC is not reachable from the controller. 

Please advise. 

Thanks 

[ammahend]

Anything changed ? SSH, https, snmp credential/permission ?

[smcisco]

No. We do not know as we enabled the notification for logs so maybe already long time. i tried to create the new credentials between WLC and DNA and then try to discover so it is showing and able to discovered but it is not reflecting into inventory. We have DNA, ISE and WLC 5520. Any suggestion would be appreciated.