No more fields or button

I tried to change filed “file upload” with a simple download link (I don’t want to use WP upload page no more).

When I saved form, all fields disappeard (I just can see “fields” title, but I can’t open it).

Front end, form is still active, but there ‘s no more form validation button.

I can’t create a new form, fields are not shown.

Is there any solution to solve this issue ?

The page I need help with: [log in to see the link]