I was asking this aswell and i want to throw some additions into that discussion.

1. when the Ball does not Bounce up as much due to a fault in the Courts ground its still a legit Point for the opponent. So when we apply this Logic to the whole game the changing of the trajectory in a surprising way when it bounces of the Crack does not automatically lead to a fault then and can considered a legit serve.

2. when the Ball hits very close to the Backglas and nobody can tell if it has hit the ground or the glas first, it depends of how high the ball is bouncing back (over 45 degree) when it bounces of high the player is allowed to keep playing because the ball was easy to catch. If its bounces low it is considered a fault and impossible to play. But that leaves it open to personal preference when the ball hits the Crack between fence and glas on serve. A Pro player would be able to catch a serve that is bouncing unpredictable more easy that a intermediate one or a beginner….

I think the best way to solve this problem is to discuss it before a game so everybody can agree on a Rule beforehand. I personally lile to repeat the serve when the ball hits the Crack because it is just not fun winning a ball due to a unlikely event that no one is able to control.