[instruments] Dashboard incomplete forms count does not match statistics page

[maximemulder]

Describe the bug

While doing my testing, the "Incomplete forms" on the dashboard indicates 11 complete forms, but when I click and go to the statistics/statistics_site/ page, there is no item to be found. I did this test as a normal user with only the "Access Profile: View/Create Candidates and Timepoints - Own Sites" permission. When I go on the same page as an admin, many items are found, including 2 of the user site.