Are you in the Steam Client Beta? Opting out should fix the problem.

you don’t need to be in the beta for this, just open the server browser, don’t wait for it to load, rightclick a server -> show players -> if it shows an empty playerlist from a server that is not empty, you will get a certain crash in the next minutes after joining a game.

right before the playerlist would load you can hear your harddisk doing something

i wish i would have recorded this, happens often, but it’s also random