@v-chuncz-msft This is an issue with the service. I already downgraded my client with no success. We use a GCC tenant. Based on the number of votes of the two "hot" issues, it's clear there is a problem.
Same issues here in a GCC tenant. The solution that finally worked for me is I cleared all data source permissions while in the April release, uninstalled, and then reinstalled the March 2021 release. After that I was able to refresh from my dataflows again.
I have only installed the april version after i discovered the error. I was hoping the old version was causing the issue. This does not seem to be the case. Clearing Data-Source privileges didnt help either.