ADDENDUM: I just noticed this calculation error seems to occur only when constants are used as inputs. For example, "=PRODUCT({1, 2, 3})" produces an erroneous result, 1; however, if you enter the values 1, 2, and 3 in cells A1, A2, and A3, "=PRODUCT(A1:A3)" and "=PRODUCT(A1,A2,A3)" both produce the correct result, 6. Hope this is helpful.
ADDENDUM: I just noticed this calculation error seems to occur only when constants are used as inputs. For example, "=PRODUCT({1, 2, 3})" produces an erroneous result, 1; however, if you enter the values 1, 2, and 3 in cells A1, A2, and A3, "=PRODUCT(A1:A3)" and "=PRODUCT( A1,A2,A3) " both produce the correct result, 6. Hope this is helpful.