We have a local Power BI Reporting Portal (used to be Reporting Service) with lots of reports both PBI and Paginated.
After latest January Power BI Server Update we are not able to change the data source for Paginated reports. Changed are just not saved without any errors.
If report was published before - it is working fine, but can't change data sources.
If you upload new Paginated report - you can't set data source for it. It will always remain as not specified.