Disappearing borders

[TOM2RN]

In my Excel 2016 form, I seem to have a disappearing border. I have columns of info that are completed using the drop down box and data validation. If I make a selection and use the auto fill, my upper and lower borders in the cells disappear. It then becomes a continuous column of info without the lower and upper borders separating the info. The side borders of each cell are fine. Why would auto fill wipe out my borders?

Thanks for any help