Attribute value not shown in Product Structure Explore

I have a problem with custom attributes inside the product structure explore app. The screenshot shows that the product has a value for the "Einkaufspreis" (purchase price) attribute. However, it is not shown in the corresponding column in the product structure explore app. This attribute is displayed correctly for other products, but then sometimes other attributes are not. 

I have already contacted our reseller, unfortunately they have not yet found a solution to this problem.