Fields that need to be fixed error

Hi guys,

I developed a few reports. Published them  and created an app.

When the users try render the report, they get an 'Fields that need to be fixed' error.(below)

When I look at the report on aap.powerbi,  all is fine.

I have a dev licence. Users  have a consummer licence.

There are  some custom visuals from the market place in the reports.

any ideas why?

Ian