Hi Catalin. Thank you so much for your support. I investigated and I:
– installed a fresh WP
– reinstalled theme and child theme
– reinstalled and activated all plugins
All was normal until here.
So I checked all values in wp_options and I finally found that the value for the key “wp_user_roles” was not the default/right/working one.
So I restored values in this key and everything is OK now.
I don’t know why this happened: maybe some active (or inactive or deleted) plugin changed that value with a “wrong” one.
Anyway I think the behavior of Visual Composer was not correct, because I was able to change a page content WITHOUT permission with the front-end editor, while there was no native “edit” link, and the normal edit backend was not accessible at all.
Maybe there is some capability not well-checked by Visual Editor? Maybe it activated its front-end editor despite lack of permission, picking up a wrong value from db?
This is the link with all my “buggy” wp_user_roles field value:
https://pastebin.com/xSib7x37
Maybe you can find out what rule allowed an author to modify other’s page content.
Thank you
G