The object 'Enemy' moves towards the center of the screen using the 'rex_moveto' plugin, and when overlapping (not collision, sorry) the object 'Player', triggers the 'moveTo' below the screen (in pixels) and is destroyed. If I hit the keys extremely fast (one of the challenges of the game) the object 'Enemy' continues his path along the X axis passing the object 'Player' and not detecting the overlapping (what I was calling collision).
I'm afraid I'm not using the proper method for this 'moveTo' because, I will need the movements (and all of its events) to be made from point A to point B, in one key press, regardless how fast the user hit the keys.
After some investigation I figured out that the reason for this is because they're set to 'Die' on collision with player but also are asked to move across X when the player presses left. This means they move and play die animation at the same time, the move angle of 0 overrides the die angle of 45. I fixed this by putting in the On EnemyMove logic, you check enemy is not playing the die animation. This works well.
In terms of the gameplay, is it not better to have the enemies moving towards the player after an amount of time, not when the player is pressing the left arrow? Although I can understand if this is just temporary functionality.