Does this error show in Power BI Service or Desktop?
Have you changed the elements in data source?
You can try to upload two tables separately without combine.
And check whether they will show error in refresh.
Please check whether your credential is correct or Expired .
Please check whether your Power bi Desktop is the latest version(2.90.1081.0).
You can update your Power BI Desktop by this link: Link. And then try again.
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.