mj61274 wrote

However, the unit in AP mode will not connect to my modem/router combo. I receive a yellow light on the mode/router port that it is plugged into confirming no connectivity.

A yellow light on the Nighthawk 1900 router's port means that you have a 100 Mbps Ethernet connection instead of a 1000 Mbps (LED would lit white). Since the CPE210 has a 100 Mbps interface only, the connection was indeed up and running. See the Nighthawk manual if in doubt about the meaning of its lights.

As for the wireless link between the two CPEs follow Johnsontp's advice of upgrading firmware first and then make sure both CPEs are carefully aligned to each other. See the Quick Install Guide on how to do this or this video if in a hurry: https://www.youtube.com/watch?v=ISUSlTcgWks

You also might get best results on the wireless link by reducing transmit power of the CPEs somewhat because of such a small distance (300 feet is not really that much for a CPE). But make sure that both devices are in free line of sight to each other.

If you have it up and running with one CPE in AP mode and the other one in client mode, you could even turn the client into AP client router mode in order to save efforts of setting up a separate router behind the client CPE.

Great to hear that it now works as intended. Have fun with your CPEs! :)