"Couldn't load the data for this visual" error for 1 user only

Jerome22 -  Assuming you have checked the RLS. Does the report has multiple visuals and only one visual is not loading?  Or the entire report is not loading? 

Please try the below and see if it works.

1) If the entire report is not loading, it might be worth adding the user to the report and dataset permissions (click on the dots and select Manage permissions on the report  & dataset), and check if it resolves the issues.

2) In the Datasource settings, check the data source credentials and see if the option "Report Viewers can only see this data source with their own credentials' is selected. If yes, then turn it off.

I added the user to the dataset , yes, this solved the issue...

but the user had access to this dataset, he can access other reports connected to it.

and can access the application deployed, so he is member of the global group in place in the company.

it's very very strange.

I'll check with the persons in charge of the security to validate all the membership of this user.