I've had that issue caused for mechanical reasons - when the score reel moves from 9 to 0, there is the most pressure on the score reel switches. They're being deflected the most going from 9 to 0 and if there too much switch tension, they fight the score reel movement and it can hang up there.
Make sure everything is clean and moving freely first, and then I've had luck adjusting the tension on the switches so they don't "fight" the score reel armature movement so much.