Hi all,
We are aware of an issue that is causing lobbies to close if a single report is made against a player or a player fails to join the lobby. We are working on this and hope to have it resolved shortly.
Valve released an update this morning which changed the format of SteamID's for TF2.
Apologies for the inconvenience. Will update this post with new information as we have it.
Thanks
TF2Center Team