Well I have to say I am more than 99% certain that is a problem with the firewall, not LFS.
That is just the kind of thing that can sometimes happen with UDP packets, due to routers or firewalls, and it's not LFS's fault when suddenly UDP packets do not arrive.
For example, if you exited LFS and restarted it, it might still not have worked, but then if you restarted the computer everything would probably work again.