The first thing you should check are the Line Complexity settings. If the maximum length of line or sidelines is lower than the longest line of your opening you are never trained in it and thus you can never reach a score of 100%.

While this reason is rather obvious there is potentially another reason, which is a little bit more complex. If you manage alternative moves for positions where it’s your turn to move you might not be trained in these alternative lines. Make sure to define these alternative candidate moves as “Best Moves” and change the training parameter for Correct Move to “All best moves”.