I had what I thought was a strange network problem. VNC Viewer (on a Windows PC) connected to a brand new Rasp Pi 3B was being continually disconnected. Putty SSH wasn't much better. When I *could* get a VNC Viewer remoted desktop that stayed open more than a few seconds, running anything like sudo apt-get update would work for a few seconds, then hang for no apparent reason.
At the same time, another VNC Viewer session to an older Rasp Pi 2 was working fine, rock solid.
Both Pi's were connected to the same Ethernet and to the same power source. A mains socket with two built-in USB sockets.
Then a dim lightbulb came on! I'd noticed that mobile phones connected to these mains sockets (with the built-in USB) took a lot longer to charge then when connected to an individual plug and USB socket.
So I changed the Pi3B's power source to an individual plug and USB socket. Immediately the Pi3B ran much better, no network problems now.
I'm guessing the newer Pi3B must draw a bit more power than the old Pi2's?