This is the line in that version that it failed: https://github.com/gjb2048/moodle-format_grid/blob/V2.9.1.3/lib.php#L1457 - that means that this: https://github.com/gjb2048/moodle-format_grid/blob/V2.9.1.3/lib.php#L1446 is false, hence https://github.com/gjb2048/moodle-format_grid/blob/V2.9.1.3/lib.php#L1417-L1443 failed.
Therefore look in the php.log file for errors. If none, then turn on developer level debugging and see if more information is there.