[Strange Error]: Unable to connect to the data source undefined.

Hello Everyone, 
I'm facing a very strange error in my scenerio.

There is one datasource which is hosted on MySQL. But I'm using two ways to import this data into powerbi.

1) my developer generated a link to the datasource which returns the data into the format of JSON. This data is before 06/04/2022. For this dataset no gateway, no credentials are needed except an Authorization key which merges with the link.

2) Server connection with MySQL connector. This data is After 06/04/2022, needed gateway and it is properly setup.

Privacy Level for both ways is "Organizational".

After importing data from both ways, I then combine them with Append Query as New.

This data refreshes correctly on Desktop but do not refreshes on Services. (Screen shot of the error is attached.)

When I upload the data before Append it refreshes on PowerBI services but not after Appending

I have tried changing Privacy Levels. But still not working. 

Everything was working fine till yesterday. but suddenly started getting this error. I'm exausted, I tried every possible thing which I could.

Any lead or help would be highly appreciated. Thanks