I was attempting the word search problem here on leetcode. Leetcode seems to give me an error for the two test cases:

board = [["a","a"]], word = "aa"

and for : board = [["a"]], word = "a"

But the following code seems to work fine on Google colab for both of these test cases. Could someone be able to pinpoint the exact cause? Likely, it is the result of the difference in Python versions. But what exactly is a loss for me! Thanks in advance!

class Solution:
    def exist2(self, board: List[List[str]], word: str, current_row, current_col,
              match_index=0,seen_cells=[]) -> bool:
        if match_index==len(word):
            return True
        else:                
            for i in range(-1,2):
                for j in range(-1,2):
                    if current_row+i>=0 and current_col+j>=0 and current_row+i<len(board)
                    and current_col+j<len(board[0]) and
                    board[current_row+i][current_col+j]==word[match_index] and
                    (current_row+i,current_col+j) not in seen_cells
                    and i+j!=-2 and i+j!=2:

                        match_index+=1
                        seen_cells.append((current_row+i,current_col+j))
                        
                        if self.exist2(board, word, current_row+i, current_col+j,
                        match_index,seen_cells):
                            return True
                        else:
                            seen_cells.remove((current_row+i,current_col+j))
                            current_row,current_col=seen_cells[-1]                            
            return False

    def exist(self, board: List[List[str]], word: str, current_row=0, current_col=0,
              match_index=0,seen_cells=[]) -> bool:
        start_index=[]       
        for i in range(len(board)):
            for j in range(len(board[0])):
                if board[i][j]==word[0]:
                    start_index.append((i,j))
        for ele in start_index:
            if self.exist2(board, word, ele[0],ele[1]):
                return True
        return False

def main()
    print(exist([["a","a"]],'a'))