Web service scheduled refreshes began failing 25 hours ago with:
Column ... contains blank values and this is not allowed for columns on the one side of a many-to-one relationship or for columns that are used as the primary key of a table.
The table referenced has simple one-to-many relationships with 2 tables. The column referenced is the only column in that table - the 1 side of each relationship.
The published dataset and source (Excel files in SharePoint) have not been touched in over a week, during which time multiple web service scheduled refreshes have run without error. A full refresh of the same PBIX file in Power BI Desktop does not reproduce this error.
The source query contained filtering to clean, trim and remove empty (to avoid this error), so I'm baffled. I've tried everything I can think of - even replacing null with "Unspecified" on both sides of the relationships - still get the same error.