Pivot table grand total not working

I have a large pivot table that works as follows:

All "Activiteit groepen" have "activiteiten"

Per activity, there are locations, and each location has sublocations. Within these sublocations there are X amount of years.

The data is the hour spent on each task. The total for each activteitengroep is working, but at the bottom the end / grand total is blank and shows nothing.


Any help is greatly appreciated!