The official multiplayer signalling server at multiplayer.construct.net appears to be working normally and has a lot of activity on it at the moment indicating a lot of people are currently using it.
I can't figure out what's going on, I tried different internet connections. I'm running the standard demo. At first, it shows:
Connecting to server... Connected, logging in... Logged in as '1232', joining room 'qwerty'... Joined the chat room as the host
Then, when I launch the second instance:
Connecting to server... Connected, logging in... Logged in as '321', joining room 'qwerty'... Joined the chat room as a peer. Kicked (either could not connect to host or host quit)
VPN is disabled, and the connection is stable. It connects to the server but cannot link the players together.