I am having the same issue as skwisgaarz this morning, woke up to find the server unresponsive and a changed connect prompt, hopped out to do an update and the server hasn't responded publicly since. It is not showing up on the in-game browser or to the Steam server browser, and attempts to connect to it by manual IP over LAN fail.
Edit:
Further information. I did the world restore even though I wasn't sure it was the problem (server not showing up, not server refusing to connect or erroring out), it made no difference, server is still not showing up, and directly connecting to LAN IP:2457 does not work.
One thing did change - directly connecting to just LAN IP without any port specified did work. I don't recall if this worked before or not, previously I always specified LAN IP:PORT+1 to connect to and it worked. It's worth noting they overhauled how clients connect to servers for this update per the patch notes. Not sure what kind of impact that would have, but there seems to be something different going on.