OpenCV unable to recognize (any) checkerboard pattern

It works with a border, to a greater degree, but our LiDAR calibration tool (ACSC) will not work if a border is present. In fact, the author of that project discouraged us from using one (ACSC uses the findChessBoardSB method).

The sine wave is a distortion resulting from re-sizing the original image. Here is a close-up: