Cannot assign more than one data acess policy to a user

When trying to assign a second data access policy to a user, I get an error saying:

> An invalid access policy assignment was detected due to duplicate entries. Please review and ensure that each assignment has a unique combination of assignmentName, policyName and ObjectId to avoid such duplicates

I have tried using both portal and az cli and I get the same error. I have tried different combinations of users, policies and assignment names (when using az cli) and all result in the same. So I think either there is a bug preventing me from assignment multiple data access policies to a user or the error and documentation is misleading.