Custom Entity - can only add existing and not add new

I have created (and tried to recreate) a Custom Entity called Salesreport..

I connected this to my Account-entity through N:N and added in the left toolbar.
When I open an account and click Sales Report, I can only choose "Add Existing Salesreport" ,
but I cannot click "Add New salesreport".

I have multiple other entities just like this, and in them - it works fine.

I can go through "Add Existing salesreport" and there click new - but that is a stupid workaround.
I am logged in as a Sysadmin , so there is not permission-issue on that end.

Please advice!