This is a typical set up for score reel switches. Check your tens reel switches. The 9 switch may be open.
Switch Zero... 1 – 8... 9
1 (top) open closed closed
2 (middle) open closed closed
3 (bottom) open open closed
On EM's, drop targets and various scoring are limited to the logic of the machine. They do not possess memory. So, if you hit another target while one is being scored, it will not register the points.