Took a wireshark trace and saw the router broadcasting with 192.168.0.1 as the source. Verified that it is the actual address by checking a known MAC address and it's IP. My local network is 192.168.1.x. I connected to it with a 192.168.0 address and set the IP back to what it originally was on 192.168.1 and it showed back up on the network. I'm theorizing that during a lightening storm the router "partially" reset itself back to factory default while leaving some stuff, like the SSIDs, in place.

I'm still baffled at how it was communicating with the Internet with a different address subnet????

Hi, well you need to connect from browser to the ip of the n750, which is 192.168.0.1 , or 192.168.1.1 Also you can connect to him via App , like Tether tp- link, i can confirm that is working from mobile phone Android.And how do you connect the router? Cable Internet direct to Tp link,? Or. Cable Internet - a box/ switch, then N750.?

And how do you connect the router? Cable Internet direct to Tp link,? Or. Cable Internet - a box/ switch, then N750.?

ISP / Cable Modem / N750

Don't know the protocols well enough to know how the N750 was talking to the internet when it had a different subnet address than the cable modem. When it was ping it was getting Destination Unknown messages. So how did it communicate? Must have been a lower level protocol?

Could you post screenshots of the whole Status page of N750 router here? Together with the Advanced Routing -> System Routing Table page.
On these two pages, we can track how it communicates with these parameters.

TPLink Admin, I will post screenshots today if I can get to it, otherwise I will asap. Something to chew on though--is it possible the TPLink router was talking with the cable modem/router through IPv6? So my cell phone, connected to the TPLink is talking IPv4 and there is somehow a conversion to IPv6 and comm is taking place that way? Tossing a theory out there in desperation!