I am also a game developer, so I understand that some bugs can slip through the cracks. But GNW Sakura was a game breaking bug that was very easy to test. All you needed to do was use her normally, nothing special, nothing hard to do, just play the game. It took me a total of about a minute to test her bug when I learned of it.
Now I can think of 2 reason why this bug slipped through, both are pretty bad but 1 is deffinitly worse.

1. You don't test things

This is a massive problem if true. I am surprised the game made it this far without testing, so it is much more likely that you don't test everything.

2. You don't test in the same enviroment as the players

This is much more likely. You probably test the game in engine before compiling and packaging it. Now this can create a lot of problems because it isn't the same enviroment as your players. You want to make sure that the play testing is done in the same enviroment as the players. Most games will package the game and connect to a test server (usually called server 0, or if public a Public Test Server/Realm PTR).

I would like to know what happened if a mod could get back to me.

Thank You