Google analytics refresh changing values

I have been trying to pull data through from a google analytics data source
however when I refresh the data I get different results everytime. I am reporting on Product SKU, Product Detail Views, Date (which I have filtered to be between 2 dates 15/06/2017-22/06/2017) and a custom dimension called customer ID. I have created a report with Product Sku and Product detail and an exclusion on a certain customerID using a report level filter. When this report is first created it appears to match what I can see in my actual google analytics dashbord however after every refresh it shows something different (typically the views decrease everytime) and then I get an error where the top line shows Product Sku as blank but still shows number of product views.

Any help with this would be greatly appreciated

Thanks