fnmI had actually finished playing a casual match and left my computer for a few minutes when it happened. It was not from competitive.
Same here.
We created a party to play casual and after we were done playing (not sure if I ranked up or not) I went afk for couple of minutes and then left the party and quit the game. After 15min or so decided to start playing tf2 again and then crashing started.
Now tf2 crashes every time just before loading mainmenu. Haven't tested much but seems to work fine on my alt account and in offline mode.
I've played a lot of competitive MM but didn't play it yesterday when tf2 started crashing only casual.
My dump: https://www.dropbox.com/s/cyk481pki6e03fw/crash_hl2.exe_20160726161725_1.dmp?dl=0