Mega Shocked (./32):Every draw type has an X,Y coordinate so it is always good practice to keep them in variables that you can print to the screen.

EX: Print Player 1 (X,Y,)
EX: Print Player 2 (X,Y)
EX: Print Scroller (X,Y)

Now you can debug your code and see if player 1,2 is moving more than the scroller is and vice versa.

Thank you. Now you can see, how insane values use to be accepted with enemyX variable after player's stepping over some places of scroller.

Mega Shocked (./32):if ((scrl_x>FRONT_MIN_X)&&( (enemyX<320) + (enemy_spr.maxWidth*16)))

I tried to use it also. Then, although a bug with enemy right shifting after right scrolling is disappeared, but enemy's "untouchable double" at the right edge of scroller appeared again.