There could be a discrepancy on the app’s total using the DateFilter when compared to the spreadsheet datasource using filters or Query statement.
It appears that when a specific (single) date is selected, no results will be displayed. Unless the said specified (single) date is set as the minimum or maximum entry in the slider - then, it will show the correct result and count (frequency).
Instead of selecting a specific date (e.g. 6/20/2017), the date slider should span 2 days or more (for this example: min. @ 6/18/2017, max @ 6/21/12017).
If there are only a couple of entries, it's best to use the categoryFilter as this displays the correct count (frequency) of the associated items for the specified (single) date.