6th gen AE dropping Internet connection

We have two late 2013 iMac's that support 802.11ac. I recently installed the 6th gen AE. After setting it up after a hard reset, all worked fine. This morning, the iMac using ac had no connection to the internet yet the Airport Utility run from that iMac showed internet connection. I rebooted the router via the Update button and the connection was restored.

Before resetting the router, I checked an older MacAir that was using the 5 GHz network on 802.11N and it connected to the Internet fine. I suspect something is intermittent or there is a bug in the ac part of the firmware.

Has any one else experienced this and/or is there any fix?

Thanks.