Problem with add new Button in Subgrid

Dear all,

i have the following Issue:

I have some Custom Entities in CRM 365 v8.2.1.411 and there are Subgrids for them in the Contact Entity. Some of them have the "+"- Add New" Button, with the Quick Create View, others are in the same way configured but the Button is not visible, and also if you click on the View, there is neither new, or add, nor delete.

I´m the Sys Admin, so this is more than strange for me, does anybody has an idea?

Thank you

Richard