The number one reason is the needle is in backwards. Two would be you hit a bad seam or your ruler and the timing is off. Third I would check the hook doesn’t have any fore and aft play, to check this take out the bobbin case put your first two fingers behind the hook and your thumb on the centre post and pull and push. There should be no play if there is you loosen the Allen screw on the collar pull the hook forward, push the collar back and tighten the screw.
Please let us know how you make out as it may help the next person.
Nigel