Mcell requires power cycle every day to regain connection to iPhones

While I didn't encounter this problem initially when I started up my Mcell a few months ago, it has now become a daily ritual that I hope someone here can help me with.

My setup:

Motorola SB 6120 modem -> Netgear WNR3500L router -> Mcell

The Mcell is connected to the router with a pair of Netgear Powerline 200 Nano Adapters because my modem and router are located in the basement with no exposure to window for the Mcell to see a GPS satellite.  The connection is good.

My Charter ISP connection is 30 mbps down and 4 mbps and is rock solid.

What's happening and what I've done so far:

Usually once a day I will no longer see the AT&T Mcell indication at the top of my iPhone 5.  When I check my wife's iPhone 4S she has also lost the AT&T Mcell indication.

Turning the phones off and then on does not bring back the Mcell connection.  Switching Airplane Mode off and then on does not bring back the Mcell connection.

The Mcell has all solid green lights when I go to check it after seeing the lost connection.  If I power cycle the Mcell, the phones will then show an Mcell connection again until the next time they lose the connection which is usually once/day but not at any particular time.

I have the latest firmware on all devices.

When I check my router's admin page after a lost connection, the router indicates that the Mcell's IP address has not changed and it remains the same after power cycling the Mcell.

On the WAN page for my router, I have set the MTU size to 1492 and set the NAT Filtering to "Open" instead of "Secured".  No improvement after doing so.

Suspicious of the Powerline Adapters, I tried disconnecting and reconnecting the Ethernet cable from the Mcell to the Powerline Adapter to mimic a temporary loss of connection to the router to see if that affected the Mcell connection.  The Mcell connection was not lost.

I have not set any open ports or a static IP address for the Mcell yet.  Is what I'm experiencing indicative of this solution?  Does anyone have any other thoughts as to what try next?

I don't want to waste my time with an AT&T Level 1 tech support person because their suggestions are almost always worthless.  I have better luck contacting user forums and that is why I'm posting here.

Thank God I was able to convince AT&T to give me a Mcell for free because if I paid $200 for it, I'd be very upset right now.

Thanks In Advance!

Avedis53