Incremental Refresh causing a refresh failure

Hi,sergej_og .thanks for your concern about this issue.

Your answer is excellent!
And I would like to share some additional solutions below.
Hello,sgallo .I am glad to help you.
As sergej_og suggested, the error message suggests that your SQL data source may not be valid. You need to check that your SQL data source credentials are set up correctly to ensure that you are able to successfully access the SQL database using the data source credentials.
Check your gateway connection to ensure that it is online and that there are no problems with the configuration information.
Try clearing your browser's cache to avoid any interference with the original data credentials information in the cache.
I hope that the following document will help you.
URL:
How to Fix Data Source Credentials Greyed Out Issues in Power BI - Monocroft
Troubleshoot gateways - Power BI | Microsoft Learn
Solved: How to correct invalid credentials in PowerBI onli... - Microsoft Fabric Community

I hope my suggestions give you good ideas, if you have any more questions, please clarify in a follow-up reply.
Best Regards,
Carson Jian,
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.