Overview:
When trying to sort a report with Group By options, the section that's expanded gets closed.
Root Cause:
Reports are re-run when sorting is applied.
Solution:
A default column sorting can be applied in the Report Builder tool by clicking the column headers, this can be either ascending or descending. Once the report is saved and run the sorting should be applied and the end user won't have to do it manually.
Related Documentation:
Vault Reporting Documentation: Creating Reports