Check and checkmate are normal because it's just way too hard to checkmate the king with dual threats.

I can't beat Alpha Beta 3 yet either. If anyone starts beating 4 I'll put some effort into optimizing the search so it can go deeper. Going 10 ply deep is pretty standard for a chess engine, so it's pretty embarrassing for humanity that nobody is beating the 3-ply setting. I think this game actually favors computers over humans more than regular chess does.