Strange Minecraft LAN connection issue

I have an odd issue with Minecraft Java Edition.
I have two computers in the house that I want to play a LAN game on.

• Both are connected to the same network
• Both have network discovery and file sharing turned on
• Both can access each other’s public folders via Windows Explorer
• Both are running Windows 10
• All Javaw.exe are allowed through Windows Firewall

So if I start a new world and ‘Open to LAN’ on ‘Machine 1’, the other can find it on the Multiplayer screen but fails to connect

io.netty.channel.abstractchannel$annotatedconnectexception

It also won’t connect via ‘Direct Connect’

If I start a new world and ‘Open to LAN’ on ‘Machine 2’, it fails to appear on the Multiplayer server screen on ‘Machine 1’, but I can ‘Direct Connect’ to it using IP/Port and it will open fine.

So obviously they can talk to other, but only in a limited capacity.
Has anybody else had this issue or could suggest a possible cause?