Yes, thats my fault, didn't notice at all :( Thank you for notice this, I think I should put some full-validation tests for my calculated solutions

Your solution 1 isn't valid, see the middle row:

[5, 6, 8, 7, 9, 4, 2, 7, 3], there are 2 7s and no 1

"The solution only need to give one valid solution" - which one?
For example, problem case from "Fixed tests":

[[0, 8, 0, 0, 5, 0, 0, 2, 0],
[6, 0, 0, 0, 0, 7, 0, 0, 5],
[0, 0, 0, 2, 0, 9, 0, 0, 0],
[0, 1, 7, 0, 0, 0, 9, 0, 0],
[5, 0, 0, 0, 0, 0, 0, 0, 3],
[0, 0, 9, 0, 0, 0, 8, 6, 0],
[0, 0, 0, 8, 0, 3, 0, 0, 0],
[9, 0, 0, 6, 0, 0, 0, 0, 2],
[0, 5, 0, 0, 1, 0, 0, 3, 0]]

My solutions:

1. [[3, 8, 1, 4, 5, 6, 7, 2, 9],
   [6, 9, 2, 1, 8, 7, 3, 4, 5],
   [7, 4, 5, 2, 3, 9, 6, 1, 8],
   [2, 1, 7, 3, 6, 8, 9, 5, 4],
   [5, 6, 8, 7, 9, 4, 2, 7, 3],
   [4, 3, 9, 5, 2, 1, 8, 6, 1],
   [1, 2, 4, 8, 7, 3, 5, 9, 6],
   [9, 7, 3, 6, 4, 5, 1, 8, 2],
   [8, 5, 6, 9, 1, 2, 4, 3, 7]]

2. [[7, 8, 3, 4, 5, 6, 1, 2, 9],
   [6, 9, 2, 1, 8, 7, 3, 4, 5],
   [1, 4, 5, 2, 3, 9, 6, 7, 8],
   [8, 1, 7, 3, 6, 2, 9, 5, 4],
   [5, 6, 4, 7, 9, 8, 2, 1, 3],
   [3, 2, 9, 5, 4, 1, 8, 6, 7],
   [4, 7, 6, 8, 2, 3, 5, 9, 1],
   [9, 3, 1, 6, 7, 5, 4, 8, 2],
   [2, 5, 8, 9, 1, 4, 7, 3, 6]]

Each solution seems work, 487 tests passed with strategy "return first calculated solution". Ironically, all tests "Now testing multiple solution sudoku!" were passed but fails on fixed and random tests. How to decide which one should be returned to pass?