I had a requirement to add contacts where the [Account Type] is “Lawyer” to entity “Case”. I created a relationship N:N between contacts and cases. Unfortunately the filter for N-N Add Existing button on a sub grid stopped working on from version CRM 2013. It does not work on CRM 2015 on Premises as well. I stumbled upon the blog Filter N:N Add Existing Lookup Dynamics CRM 2013 how to resolve the issue using the CRM function** LookupObjectsWithCallback.