i have found that many of the replacement drop targets are warped/curved which causes them not to be secured in the up position or bowed to the point of contacting the playfield when in the up position, since you have several sets use only the straightest of them - you can try to straighten bowed drop targets by heating them in boiling water and bending them back straight, new springs are a must and like others have mentioned install drop target mechanism pushed towards the back of the playfield to maximize the distance between the target & playfield

i wouldn't start drilling holes to move the whole drop assembly tho