Why Did My Moodle Due Dates Change -

we have due dates set on of our assignments 11:55pm. noticed of our due dates changed 7:55pm on assignments (the dates stayed same, time changed). happened in of our courses, not isolated single course.

so why 4 hour change? double checked server time , correct, profile time set correct well. idea how or why happening? don't want happen.

we using moodle 2.8.1