Fiora's passive is not doing anywhere near the intended amount of damage, it seems like a decimal point or a zero is misplaced somewhere.
1. Choose Fiora
2. Build enough AD so that the damage of your passive should be easily visible
3. Attack a vital on a target dummy or a champion, it works on both
4. Notice the white true damage number being significantly lower than it should be according to the passive scaling
Here is a video showing the bug on both a target dummy and a champion. https://www.youtube.com/watch?v=ExEDN9I8pzs&