LAN multiplayer not working

Put the summary of the bug you're having here

What I expected to happen was...:
Join a LAN multiplayer world

What actually happened was...:
neither one of our computers can see each other on LAN multiplayer. works fine on 18w43a/b. we have tried leaving the world and restarting game etc. we have also tried switching which computer its the host and checking the internet connection.

Steps to Reproduce:
1. host a lan world on one computer

2. the other computer doesn't pick up any LAN Worlds