When you say that it no longer works, what happens? The form doesn't display on the front end at all, is broken, or the shortcode is shown on the front end?
Is this a form you made with the visual editor or with the advanced editor.
If you make changes with the advanced editor, you'll notice that the form itself is made up of shortcodes, and some of these are required.
The first step I would take would be to make a new dummy form in advanced mode and compare the problem form to see if some of these shortcodes are broken or missing.
If you can't identify the problem yourself, could we take a look at your site?
Let me mark your next reply as private so that we can get log-in credentials from you—you may want to create a temporary admin user for us to use that you can later delete. And be sure to have a current backup of your site.
Can you also confirm which form you refer to, and where it is displayed.
Thanks for the details, I can login into your website.
Which one is the "my account" page?
I assume we are talking about the page "Mon compte": hidden link
It works fine in my Chrome browser, I can see the editing user form correctly, see my screenshot userformcompte.jpg
Is this issue resolved? or is there any missing steps?