What do you mean a dead zone?Could you share a screenshot of the screen where you placed your monster (in NESmaker)?
Your monster tiles and color palette are set correctly on the first screen ? Remember, for scrolling screens, the monster that will be loaded (monster goup) are the ones assigned to the 1st screen of the scrolling segment.
Also, don't forget you have a dead zone with the scrolling screens (the left half part of your 2nd screen).
Basically their is a point in the screen where sometimes it doesn’t spawn monsters, it’s kinda wack