Windows – Cygwin X doesn’t work with DISPLAY localhost:0 on windows 10

I had Cygwin X 64 bit running fine on Windows 7. I upgraded to Windows 10 and things stopped working.
So I wiped out the Cygwin and installed again from scratch. I installed Cygwin X 1.18.4 (x86_64). I started X server using startxwin. I could only get xterm to work when I set DISPLAY=:0.
If I set DISPLAY=localhost:0 I get can't open display.

Also I can't have another computer throw a xterm back to Cygwin X. I get same error. I even tried throwing xterm to a Linux host and that gave same error. Windows firewall is turned off and I set xhost + on all hosts.

Any advice on why I can't explicitly set the DISPLAY to localhost or the local IP of my computer?

Thanks