When creating an ad-hoc report using weekly periods, the data warehouse is starting on Monday.
However, in Modern UX as well as fiscal periods, the weekly dates start on Sunday.
Why is there a difference?
This may be caused by the Weekly Data Warehouse slices and the First Day of the Week are set to Monday, where the fiscal weekly periods start on Sunday.
Release : 15.9.3
Component : CLARITY DATA WAREHOUSE
If confirmed that the First Day of the Week can be changed do the following:
Now the Week Start will be Sunday for and ad-hoc or reports.
The only caveat here is that in Classic, the weekly TSV always start on Monday.