Here is my scenario, I have entity A where the user has read, append, and append to rights. Entity B, the user has all permissions except delete. Previously in CRM 2015, when the user pulled up entity A form, they could go down to the subgrid which contained Entity B and click the plus and add a new record. After the upgrade and turning off turbo forms, the plus is gone and the form is read only. If I enable turbo forms, the form shows the add button on the subgrid. I gave the user write privilege on entity A as that was the easiest fix for the moment.