FCC sudoku solver example has faulty logic

I was playing around with the FCC sudoku solver example when I stumbled upon faulty logic. A simple change to the initial string (…9…5[truncated]) in cell A2 to (.99…5[truncated]) results in a solvable puzzle when it shouldn’t. Somehow this app also passes all the FCC tests despite the faulty logic. Maybe you guys can take a look at the issue?

Edit: Another faulty “solvable” string is ([truncated].3…6.4), where cell I9 has been changed from “.” to “4”.

Challenge: Sudoku Solver

Link to the challenge: