Pivot Table/Slicers Skipping Month

Thanks. I didn't create the workbook, so not seeing how the month number switched over to the three character month name. What I did notice is the when I clicked the "Month" dropped down (where I could select specific months to see/not see, all the months were in timeframe order with the exception of Oct and Nov. So it looked like Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Nov, Oct, Dec. Couldn't figure out why that happened or how to fix it. I just added a new column that calculated the three digit month name based off of a date field in the data. It then displayed the information fine.