Dear Jeroen,
Before investigating, make sure that you have latest version.
To validate which version of Report Builder you have:
1. Login into Report Builder in Excel
2. Navigate to Add-ins > Options.
3. Make sure you use 5.6.21 or higher.
To upgrade your Report Builder version:
1. Login to Adobe Analytics
2. Navigate to Tools > Report Builder
3. Choose 32-bit or 64-bit, based on your Excel version. This can be validated in Excel under File > Account > About Excel. The version is listed at the top.
4. Close Excel, and install the .exe file that is downloaded.
If you have latest version with proper installation based on 32-bit or 64-bit Excel, kindly reach Adobe Customer Care : CustomerCare@adobe.com
You should be supported user for Adobe Analytics to reach Customer Care. If not, reach your Adobe Account Manager.
Thank You
Arun