workspace cannot be reassigned because it includes Fabric items or you're attempting to move them

Hello,

We are using powerbi premium capacity, to embed reports into our web app. Recently we tested some of the features Microsoft Fabric offers. After the trial ended we deleted them, but suddenly the workspace was assigned to Pro instead of capacity. Now we are unable to reassing it. 

We have the following error:
workspace cannot be reassigned because it includes Fabric items or you're attempting to move them across regions. This is not supported currently. Remove the Fabric items, or move the workspace within the same region, and then try again.

How to identify, what are those items, and reassing the workspace?