Same for me in TestCase #6:

Here I am:

0 0 0 0 0 0 0 0 0 0 0 0 1 x 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0
0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 1 1 1 0 0 0 0 2 x 2 1 x 1 0
1 1 1 0 0 0 0 1 1 1 0 0 0 0 1 1 2 x 1 0 0 0 0 2 x 2 1 1 1 0
1 x 1 1 1 1 0 1 x 2 1 1 0 0 1 x 2 1 1 0 0 0 0 1 1 1 0 0 0 0
1 2 2 3 x 2 0 1 1 2 x 1 0 0 1 2 2 1 0 0 0 0 0 1 1 1 0 0 1 1
0 1 x 3 x 2 0 0 0 1 1 1 0 1 2 3 x 1 0 0 0 0 0 1 x 1 0 0 1 x
0 1 1 3 3 3 2 1 1 1 1 2 1 2 x x 2 2 1 1 0 0 0 1 1 1 1 1 2 1
0 0 0 1 x x 2 x 1 1 x 2 x 2 3 3 3 2 x 1 0 1 1 1 0 0 2 x 2 0
0 1 1 2 2 2 3 2 2 1 1 2 1 1 1 x 2 x 2 1 0 1 x 1 0 0 2 x 2 0
1 2 x 1 0 1 2 x 1 0 0 0 1 1 2 2 3 2 1 0 0 1 1 1 0 0 1 1 1 0
? ? 2 1 0 1 x 3 2 1 0 0 1 x 1 1 x 2 1 0 0 0 1 1 1 0 0 0 0 0
? ? 2 1 2 2 2 2 x 1 0 0 1 1 1 1 2 x 1 0 0 0 1 x 2 1 0 0 0 0
? ? 2 x 2 x 1 1 1 1 0 0 0 0 1 1 2 1 1 0 0 0 1 2 x 1 0 0 0 0
? ? ? 2 2 1 1 0 0 1 1 1 0 0 1 x 1 0 0 0 0 0 1 2 2 1 0 0 0 0
? ? ? 1 0 0 0 0 0 1 x 1 0 0 1 1 1 0 0 0 0 0 1 x 1 0 0 0 0 0

3 mines left.
Why isn't it expecting '?'

if (answer) return answer;