I'm trying to play a LAN server with my sibling, but every few minutes, I lag then get disconnected. It tells me that the connection was forcibly closed by a remote host. We have the same wifi, and also I have let Java through firewall on both computers. We run 1.10.2 and Windows 10.
Try using your public IP adress instead of a local one
I have the same problem that you describe with a computer in my local network. I tried every solution that came to mind like completely uninstall java then reinstall, update graphic card drivers, open ports through the firewall but NOTHING worked.
The solution I found and that seems working really fine is that instead of using your local ip address where the server is located (example: 192.168.1.103) for the server, use the public address (example: 184.108.40.206)
You can find your IP adress here