Mashup Error - effectively not signed into Power Query. Multiple user issue?

Hi All, 

I have an issue (See pic) with some Power Query workbooks. I've had it before, and it basically requires going into Data source settings and resigning into sharepoint/datasource and making sure Privacy is set to Organizational.

At least that's what's worked for me in the past. I've only had a it a couple of times, and doing it once seems to sort it for a long time.

I now have a user who had the error last week. I got her to resign in and checked all her permissions. Everything worked. 

Now this week the error has returned immediately. 

The queries are just simple filters of a workbook all within the same sharepoint space which user has full access to.

Apologies for vagueness.