There's an issue with the game, it's being talked about on reddit, the beta forums,.. but not here.

People with low upload bandwidth will have encountered situations in which they pretty much time out, can't interact with the map or opponents anymore. First you can jump around alright, but there's no item pickups, no projectiles (nailgun, rocket) coming out of your gun until the game catches up and all your actions get added to the gamestate with a huge delay all at once (it seems).

On the scoreboard you'll notice 255 ms ping for the duration.

Comments seem to indicate that capping your FPS might alleviate the situation.

Please post here if you are effected by this.