Expansion of the brick most likely. Repetitive movement of the foundation doesn't help things but this is more of a brick defect than foundation. It's hard to keep corners together if the bricklayer doesn't lace or interlock the courses. Ninety degree angles are easy to lace but 45's and others are harder to lay for the mason. A good one or one who is paid well will take the time needed to make the return look good by interlocking the corner instead of having a joint at the corner. This one didn't for whatever reason.