It's never happened to me, but at least 3 people crash every time I load into an ARDM game. It seems to happen right at that loading bar where the game seems to be calculating all of the random heroes that your team will be receiving for the game. I'm guessing that the calculations involved in figuring out which random heroes you get is a bit too much for what it should be. Maybe those calculations should start being done server side, or something else needs to change since some people's hardware may not be able to handle the sort of load it is trying to throw at their computer.
They aren't calculating what heroes will be picked, they are loading the models to all the heroes. They can't do that server side.