Windows 10 edition unable to load Friend LAN game

Last night, everything worked.
My son loaded up the world we've played in 100 times on his Samsung Note A tablet.
I opened minecraft windows 10 edition on my windows 10 laptop.
I can see his session come up on the list and select it.
The screen flashes "locating server", then I just get a blank screen.

I've attached screenshots below.

No error messages appear, no indication of anything happens.