Hi Taylor,
I found out what caused the problem: I am using the plugin Polylang. When it is activated, I am unable to create a new form or to change the name of an existing one. Performing other changes works, thought.
And this happens always, even if I uncheck the box “Forms” for the Polylang options (Polylang aims at providing multilingual websites and can also translate forms).
When the Polylang is deactivated, I am able to create and modify forms. And I’ll do that, your plugin is great to use!
For future references, there were no conflict with my theme (Divi 2.2 from Elegant Themes) or the other plugins used (Akismet and UpdraftPlus).
Thanks again for the great work,
Nicolas