Workflow SP 2013 - Cannot retrieve a UserMulti Field value

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SharePoint2013

Hello,

I'm developing a SharePoint-hosted App with a workflow working with a List that contains a UserMulti Field. I'm currently trying to retrieve this field value to a variable with a GetDynamicValueProperties but this isn't working, the workflow execution is hanging.

My workflow configuration is OK since I can retrieve the Title to a string variable for example but when I try to get the USerMulti Field (called 'Members') to a Object variable, nothing happen.

After setting up my environment to catch the HTTP traffic I was able to find something in the XML conversation :

<WorkflowStatusDetails>RequestorId: d05baf50-adbc-6aa7-0000-000000000000. Details: RequestorId: d05baf50-adbc-6aa7-0000-000000000000. Details: An unhandled exception occurred during the execution of the workflow instance. Exception details: System.InvalidOperationException: Looking up a value using a key is not supported on an instance of 'Microsoft.Activities.Dynamic.DynamicJsonPrimitive'.
   at Microsoft.Activities.Dynamic.DynamicItem.TryGetValue(String key, DynamicItem& value)
   at Microsoft.Activities.Dynamic.DynamicValueBuilder.PathSegmentFactory.ObjectPathSegment.Get(DynamicItem obj)
   at Microsoft.Activities.Dynamic.DynamicValueBuilder.PathSegmentFactory.ObjectPathSegment.Get(DynamicItem obj)
   at Microsoft.Activities.Dynamic.DynamicValueBuilder.PathSegmentFactory.ArrayPathSegment.Get(DynamicItem obj)
   at Microsoft.Activities.Dynamic.DynamicValueBuilder.PathSegmentFactory.ObjectPathSegment.Get(DynamicItem obj)
   at Microsoft.Activities.Dynamic.DynamicValueBuilder.PathSegmentFactory.ObjectPathSegment.Get(DynamicItem obj)
   at Microsoft.Activities.GetODataProperties.Execute(CodeActivityContext context)
   at System.Activities.CodeActivity.InternalExecute(ActivityInstance instance, ActivityExecutor executor, BookmarkManager bookmarkManager)
   at System.Activities.Runtime.ActivityExecutor.ExecuteActivityWorkItem.ExecuteBody(ActivityExecutor executor, BookmarkManager bookmarkManager, Location resultLocation)</WorkflowStatusDetails>

Can somebody enlighten me on that error or how to properly use a UserMulti Field in a Workflow ?

Thanks and regards.