@Stick-E-Paw 

The inability to not be able to ping a computer may be that something is being filtered on the computer end.

Connect your smartphone, and test ping that device as well.

The settings you have tried are pretty much all you can do. 

Another thing you can possibly try is to set the CR700 to bridge mode, connect one of the computers, and test that connection. 

The last thing to evaluate is the computer security settings.

In the past users have ran their computers on safe mode to see if any software may be getting in the way.

@Stick-E-Paw I just got this modem/router and I'm having the same issues. I have Call of Duty: Modern Warfare on PS4 and PC. On PS4 I can't connect to online services and on PC Battle.net doesn't work at all. However, one i turn on my phone's hotspot everything seems to work fine but I obviously can't use the hot spot to play because it's too slow and won't last long. Also it's not a wifi issue, literally everything else works fine this modem simply won't let me connect to those specific servers.

@Tony please read my reply to Stick-E-Paw, thank you.

@Stick-E-Paw This Is also happening to me but for xbox one, any solutions?

I've had various issues with my CR700, that I bought used off eBay recently.  The wireless 2.4G cuts out after a few days, and I was unable to connect to League of Legends, and some other services, that sound similar to the troubles mentioned in this thread.  Most of it cleared up when I did a hard reset on it.  That wasn't entirely trivial, I think I had to hold the reset down for a full 10 secs or so.

Since then, no real problems, but the 2.4G cut out again.  The reset had put the power save back on for that as well as some channel width suggestions from another thread, so I'm reinstating those again and hoping it'll be good from now on.