Xming not working with Cygwin

I have two Windows 10 machines with Cygwin + Xming, one of them works fine, but I can't get the other one to work, if I try to start ddd for instance, I get:

Error: Can't open display:

If I manually set $DISPLAY it works, but X11 forwarding from remote hosts doesn't

The second machine works flawlessy, $DISPLAY is automatically set and X11 forwarding works.

PuTTY is NOT involved in this setup

Xming is running in both machines in localhost:0.0

I've been trying for a while and I might've forgot to check something, but I can't get it to work :(

Any ideas?

Thanks

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