Valve just sent out word that they are going to be performing maintenance on their server backend today at 3:45PM (PT). They said that this will affect multiplayer in negative ways.
So, just in case things start to get a little weird later, you'll now know why.
Connectivity to official and community game servers will be affected, game lobbies, matchmaking, inventories and weapon loadouts will be unavailable for the duration of this maintenance.
Previous build of the game client will not be pinned due to compatibility issues and all clients and game servers will be required to update to the new build after the game update is released.
Previous build of the game client will not be pinned due to compatibility issues and all clients and game servers will be required to update to the new build after the game update is released.
So, just in case things start to get a little weird later, you'll now know why.