MSM 720 loses connection with DNS

[idareval]

I have a MSM720 controller with the following scenarios.

4 networks with DHCP and Active Directory authentication
1 network with DHCP and WPA2
1 network with DHCP and authentication HTML

The solution works well, but is being presented that the controller loses connection to the internal DNS and authenticated users with the DA can not connect. This does not happen periodically.

The way to achieve communication again is to delete the DNS, save the settings and create them again.

Thank you very much.