Power BI source step reading excel file showing inconsistent format

Hi, I have a monthly power BI report that gets updated each month. It reads excel file which is outputted by SAS. The format of the excel file for different months should be the same. But the query fails when I try to use last month's source step to read this month's data.

I figure that this has something to do with the excel files. My excel files from last month is much larger than this month's, but by visual inspection I cannot find any difference. The first screenshot is the source step after reading in last month's data, and the second screenshot is the source step after reading this month's data. I notice that last month's has three more columns : Item, Kind, and Hidden. Do you know what this imply about the the excel files and how I should modify this month's excel file so it can be read in the same way? Thank you so much!