The position of the day can't suddenly drop to zero. Even on the last trading day, there will still be some positions. If it is always 0, it means that this contract has expired and delisted.
Tell me more about your opening and closing positions. If you don't have a lot of hands, it won't affect the change of the position pattern at all, but the influence still exists: closing yesterday's long position may be 1, which will reduce the total position by a corresponding number (at this time, there will be corresponding short positions) and lower the position line, or 2, the total position remains unchanged (at this time, you close the position and give a corresponding number of new long positions), which will make the position line level, or 3, the position line is 60.