There are a lot of things that could be an issue, a good place to start is with the unleashed troubleshooting guide which is here https://docs.arris.com/bundle/unleashed-200.7-troublshootingref/page/GUID-897F2363-D881-4E84-B7C3-E6...
The full user manual is here https://docs.arris.com/bundle/unleashed-200.6-onlinehelp/page/GUID-8C585237-6DE8-4CEC-A4EF-E06E1B1B3...
Do you know if the AP that is not working has obtained an IP address?
If it has, are you and to ping it when connected to the SSID of the AP that is working?
If the answer is "no" to either of those questions then you may have a problem with the 7150 configuration.
If the answer is "yes" to both questions then the problem is with the APs and the unleashed configuration.