Like the others, Pistol, I'm gonna guess that your 2018's are a bit stiff for your bow. Field points are rather forgiving of tuning compared to broadheads. Couple of things you can try just to confirm this: 1) find a couple of heavier points and try them out. You should see some improvement if spine is the issue. 2) Shoot what you have through paper from about 6 feet, both field points and broadheads. The tear in the paper will show you how the arrow is coming off the bow. Assuming a right hand shooter, if the point is to the left of the fletching the arrow is too stiff. Newspaper works great; set it far enough in front of the backstop/target so that the arrow clears the paper before hitting the target. A vertical tear is usually a nock point issue and an angle tear is some of both.
You can also swap broadheads around or clock the inserts so the blades are horizontal. This can reduce the initial planing and bring the broadheads back into the group. You haven't really fixed anything, it's just another indication that there is a spine issue.
Good luck and keep us posted.