There is a bug whrere when loading in to a new match
(either by finishing the previous one and switching map or when joining a new lobby), you can't select or see the different classes. You can still see the map and when the round starts even spectate, but you yourself cant select a class, switching sides does not fix it. I usually could fix this by looking for a new match or sometimes I had to restart the game. It happens randomly, before the last update (1.6.3 the one that finally fixed smoke) it happened about every 15 to 20th match, after the update it happens about every 2nd to 8th match.