I can only create one form?

This is a little bit wired for me. It seams, I can only create one form.

– creating a form (which will have the id eg. 330) [contact-form-7 id=”330″ title=”form01″]

so long all works fine.

– If I click “Add new” I see the page “edit contact form” with the line “[contact-form-7 id=”330″ title=”form01”] – Changes I made are really editing the first form

– The same happens, if I am on the form page and select “duplicate” underneath my form01 -> “edit contact form”. Only the form name became a additional “_copy”

– If I am on the edit page and click right hand “Duplicate” (over “Save”) the same behavior: The name becomes again a “_copy” added, bit I am in Edit mode and the shown id is still “331”

I also uninstalled the plugin and installed it again.

WP 5.4.2–de_DE
Contact Form 5.2
PHP: 7.4
Theme: PRO von theme.co

Any ideas?
Thank you,
mickna