After a great deal of even deeper troubleshooting, disconnecting, wire chasing, etc., etc., etc... I have specifically located the problem on the shorting light. As it turns out, apparently, on the center (screwable) mounting of the middle sconce the threaded pole chafed the black wire of the Romex and made a good contact between it and the ground wire -directly adjacent to it. I have pulled though additional wire, reconnected all lights, and have applied the power (with all grounds in-place/connected) and everything appears to be working as advertised.
And so, we are now faced with what I hope will be the only thing left in this electrical debacle... that of returning the control of the controlled receptacle BACK to the corresponding switches.
Here's the short of it...
If you remember, we took the (middle) 3-way Switch (Romex/cable #2 & 3) out of use from being one of the (dual) controlling switches that controlled the two-outlet Receptacle (across the Living room); this was done in order to use it as the single controlling switch for the sconce lighting (on the Lanai).
The remaining (first 3-way) controlling switch, located at Switch Panel #2 was then to be the only switch controlling the controlled Receptacle.
Currently, we are left with a receptacle that has power coming into (present) at both the Black junction/wires, as well as the Red wire, attached to the receptacle; however, there is no power at the receptacle itself.
I think, if I look closely, I can see the Finish Line ahead. And now we just need to tap that electron-filled brain of yours (hopefully) one more time to resolve this last equation.
So, what say you about getting power to the receptacle, and making sure that our switch at Panel-2 function to operate same?