Error mapping user in connection to on-premise SSAS

We have a connection to on-prem SSAS that is failing refresh. After adding the mapping for the user to convert [email protected] to AD\user.name it is still failing although the error in the refresh now reads as follows:

This is odd because I have not added two \\ in the mapping and the test at the gateway datasource looks fine.

Data source error{"error":{"code":"DM_GWPipeline_Gateway_MashupDataAccessError","pbi.error":{"code":"DM_GWPipeline_Gateway_MashupDataAccessError","parameters":{},"details":[{"code":"DM_ErrorDetailNameCode_UnderlyingErrorCode","detail":{"type":1,"value":"-2147467259"}},{"code":"DM_ErrorDetailNameCode_UnderlyingErrorMessage","detail":{"type":1,"value":"AnalysisServices: Analyseur XML for Analysis : La valeur 'DIR\\user.name' de la propriété XML pour Analysis Services 'EffectiveUserName' n'est pas valide."}},{"code":"DM_ErrorDetailNameCode_UnderlyingHResult","detail":{"type":1,"value":"-2147467259"}},{"code":"Microsoft.Data.Mashup.ValueError.DataSourceKind","detail":{"type":1,"value":"AnalysisServices"}},{"code":"Microsoft.Data.Mashup.ValueError.DataSourcePath","detail":{"type":1,"value":"vd522703;Pioneer_Analysis"}},{"code":"Microsoft.Data.Mashup.ValueError.Reason","detail":{"type":1,"value":"DataSource.Error"}}],"exceptionCulprit":1}}} Table: XXX

Does anyone know if this a bug or how to resolve?