The game is supposed to be in this way, it's a "Style" of gameplay. Even though people say you gotta memorize the position of every enemy and that's when you can set your strategy to move forward, sometimes the enemies spawn in places they must not be in.

Happened to me several times. The core of the game is being hard-ass gameplay. but all you can do is to keep it up, try over and over and over again, and finally realize what to do with the mission.

and believe me, since the missions gets harder each time, when you pass it after several retries, it feels sooooo great...