Hi Leo. Thanks for the answer.
No, not that much. Besides GP Premium, I have these plugins installed and active: Akismet Anti-Spam, Classic Editor, Slimstat Analytics, Page Builder from SiteOrigin, SiteOrigin Widgets Bundle and Sydney Toolbox.
I ran some tests and I realized that the GP Premium only works when the Page Builder from SiteOrigin and SiteOrigin Widgets Bundle plugins are deactivated. And also, and unfortunatelly, only when the Classic Editor plugin is off.
Thanks again for helping!