Quoted from DaveH:

No, it would more be considered a manufacturing flaw. And the fix takes about 20 seconds. Open up the game, slide the playfield out, grab a ball, walk to the left side of the machine near the castle playfield. Right at the top of the loop there is a wireform, and on the ones that reject it is just a bit too low. Measure it against the side of a ball, then slide your finger under the wireform and pull it up a bit. Then measure again with the ball. Once you get it high enough the ball will just glide in that loop. Put the ball back, close the game, and the rejects will be down to a minimum (you still have to hit the shot).

Quoted from DaveH:

And the fix takes about 20 seconds. Open up the game, slide the playfield out, grab a ball, walk to the left side of the machine near the castle playfield. Right at the top of the loop there is a wireform, and on the ones that reject it is just a bit too low. Measure it against the side of a ball, then slide your finger under the wireform and pull it up a bit. Then measure again with the ball. Once you get it high enough the ball will just glide in that loop. Put the ball back, close the game, and the rejects will be down to a minimum (you still have to hit the shot).