Trying to design a form Sharepoint with Nintex Form Designer. When I try to edit control settings ex in a Single line text (element on a list) - Ok for open the settings  but the button  Save ir Cancel are gone (in general) ?

It should have been shoven:

But it shows me (very, very short it shows me the button)

What's is wrong

NB! when I open the form designer  - we Work with Classic forms