findChessboardCornersSB not working, detects only some corners

Hi.
I have pictures of my checkerboard, but findChessboardCornersSB() or findChessboardCorners() cannot detect all corners, only some of them, or none, regardless of checkerboard dimensions that I input.

I tried these options:

# Try finding the chessboard
chessboard_size = (6, 7)

flags = cv2.CALIB_CB_EXHAUSTIVE + cv2.CALIB_CB_ACCURACY

flags_std = cv2.CALIB_CB_FAST_CHECK + cv2.CALIB_CB_ADAPTIVE_THRESH

# flags_std = cv2.CALIB_USE_INTRINSIC_GUESS

ret_sb, corners_sb = cv2.findChessboardCornersSB(img_8bit, chessboard_size, flags=flags)

ret_std, corners_std = cv2.findChessboardCorners(img_8bit, chessboard_size, flags=cv2.CALIB_CB_FAST_CHECK | cv2.CALIB_CB_ADAPTIVE_THRESH) # Standard method

also posted here

https://stackoverflow.com/questions/79685744/cv2-findchessboardcornerssb-not-working-detects-only-some-corners