When trying to test RLS with my manager, we found he is unable to connect to a data source that has RLS, trying both the Analyze in Excel from the PowerBI service as well as the new BI Publisher for Excel. In both instances with the RLS enabled datasource, an error is received in Excel that says "The following system error occurred:" (no error is actually listed) and then prompts him to log into the service again, which is unsuccessful.
He successfully used both features on a non RLS enabled datasource, so the issue appears to be specific to RLS.