I don’t understand why one device (thinkpad) in LAN see only devices inside the LAN (it don’t see the 2 outside)…and report “Connection to … closed: reading length: EOF” in the log:
The others 2 in LAN see all device (inside and outside), here an example, with same version of Syncthing:
The router seems works good. I have also try to using smartphone as hotspot (ie. put device outside the LAN), but the thinkpad see only those 2 devices.
Please post full screenshots of the Syncthing Web GUI from all devices. Are all of them located in the same network? Are you using the default settings, or have you, by any change, modified some of the network-related options, e.g. regarding discovery, relaying, etc.?