In my experience (I upgraded computers and Ram from initial play of ZH to now) crashes occur with large maps + many players + many units needing micromgmt. In short, the more activity you stress your particular game with, the more likely you'll run into the serious errors. I suspect those who complain the most have a) older comp/less Ram and/or really like to micromg against a lot of players.
I still get serious errors now and then, but it's pretty rare. I am focusing on games of 1 (me) vs 3-4 (allied AI players.)
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