I’m running MS Excel 2016 and the latest version of Powerpivot. In the older versions I didn’t experience this problem.
Basically, when I go to copy/paste a dataset into Powerpivot it somehow does not copy some of the date data. It typically does it if there is a date in the first column, however, now I’m noticing that it will randomly exclude dates from other columns. It’s only for some rows of data, not the whole column.