@jas00 

Is the NVR attached to the router or the AP?

Can you get to the NVR/DVR using an IP address (192.168.x.xxx)?

Are you using address reservation and port forwarding?

@jas00 

NVR is connected to router (wired connection).

Yes, I can get to the NVR using the local IP address .

I'm using port forwarding (Hikvision NVR):

HTTP port 80

RTSP port 554

Server port 8000

camera 1 port 65001

camera 2 port 65002

camera 3 port 65003

Not using address reservation (Hikvision IP fixed not conflicting with DHCP range).

to further clarify.  I use IVMS-4500 app to access cameras on android mobile.  I can create two devices, one using DDNS address (name.tplinkdns.com), and one use local IP address.  On LTE network, and connected to router WiFi, both devices can see cameras.  Connected to AP WiFi, only local IP device can access cameras.

@jas00  Unfortunately, this is one of the (many) issues with the firmware of this "premium" router from TP-Link. NAT loopback does not work on the same network (though I have had it work from LAN -> WIFI. Sometimes the router needs a reboot to make it work.) @Tony and the rest of the TP-Link team have just dropped the ball on this product. Wifi sucks also, my 2 year oldER ASUS router is better. I would return it :(

@makeIThappen 

Thanks for the response.  I'm really disappointed with the router.  I actually purchased it for it's WAN LAG capability, but that never worked.  My ISP is Comcast with 1.2Gbit service and my modem is a Motorola MB8600 that supports LAG.  I quickly gave up on that because I got no help from TP Link.

Later my wife complained about not being able to see our security cameras on her smartphone when she was in the main part of the house (access point WiFi connection).  I've gone round and round with TP Link support, but all they do is try to blame some other component in my network.  Never had any problem when I was using an Archer A7 router.  Upgrading to the C5400X was a mistake.

I did get it to work once after a reboot of the router, but haven't been able to repeat this.