Could it be https://github.com/python/cpython/blob/master/Modules/mathmodule.c#L2565

When 0 is in the iterator, i_result get sets to 0 and then on the next iteration x/i_result is 0/0 which is undefined behavior?

C99 6.5.5p5 - The result of the / operator is the quotient from the division of the first operand by the second; the result of the % operator is the remainder. In both operations, if the value of the second operand is zero, the behavior is undefined.

I will do some tests, if it's that I will post a patch.