Hi, it appears that I'm somehow losing packets. (For example: I switch from day to night and one of the connected machines stays in day mode)
Now I thought that this can't happen with TCP, isn't TCP guaranteeing that every packet arrives? (unless of course there's no connection)
How is TNet handling this? What happens when a packet can't be delivered? Will it re-try? When will a client disconnect?
Can you fire up wireshark on both the sending and receiving machine to verify the packet is indeed being dropped?
What I think is most likely happening is that the packet is arriving, but your RFC doesn't do what you intend it to do. You could place a breakpoint or a Debug.Log at the very top of your RFC to verify that it's being called. If it's being called then the packet has arrived and has been processed.
As for your follow-up questions, I'd have to dig into TNet to answer [which you can do as well, mind you

]. Perhaps someone else will be able to answer those questions.