N600 C3700 - Clients lose connectivity and unable to reconnect with correct passphrase

I bought the C3700|N600 from Amazon around April 2016 and left it in the box for about a month. Switched from AT&T UVerse to Cox and the Cox technician installed the C3700 and performed the initial configuration while I was at work one day. I changed the SSIDs, passphrases, and looked at the rest of the configuration interface a few weeks later, but left everything else as originally configured. I didn't really notice it at first, but it seems like everyone in my family were having connectivity problems from the beginning. I believe the PS3 physically connected to an 8-port 1GbE switch that is connected to the C3700 has worked flawlessly. All 2.4Ghz wireless connections (three iPhone 6 devices, a MacBook Pro (El Capitan), two Samsung DVD players, and one Amazon Fire Stick) had fairly good signal strength when connected, but would occassionally disconnect from the C3700 wireless. We would attempt to reconnect and type in the passphrase over and over again and always received an error stating "Incorrect password for <SSID>. The SSID was available and still had a strong signal. The only way to resolve this was to reboot the C3700. It seems that this happens at least once a week. I changed the 2.4Ghz channel last night in hopes that would resolve the problem, but it seems to continue today.

This may be unrelated, but our 2.4Ghz wireless speed was sub 2Mbps when I tested last night. Cox Preferred is a 50Mbps down connection.

Also probably unrelated, but our 5Ghz wilreless range is pretty much contained to the room that the c3700 is located in, so we don't use it very often.

I would appreciate any comments and/or recommendations on how to resolve this issue. I haven't contacted Cox support yet and I believe the Netgear support has ran out.

-Robert