We run into a bizarre problem where the first column in the spreadsheet (the date column) gets corrupted. Sometimes a date gets repeated twice; sometimes it gets eliminated entirely. Here's a couple screenshots of the first two columns, first in the original, second in the Sisense import showing the problem.
Sisense after import:
As you can see, 11/4 gets repeated, 11/6 disappears, 11/7 gets repeated, and 11/9 disappears.
These problems are scattered seemingly at random throughout the Sisense import; approximately 1 in 20 records is altered.
Check your language settings on sheets. Also, make sure you format the dates correctly or try to format as text.