I can’t seem to update old pages and create new one. All changes made or elements added disappear after saving.
Thanks for asking your question at Envato forum.
Contact you Item Author
If they ask about purchase key then collect from Here
Still have any question open a Envato help ticket from Here
If you are running wordpress 5 then you can try to install classic editor, hope will fix. If still not then please check compatibility your theme version, page builder version, wordpress version, is there any compatibility issues (going through your theme details page at themeforest)? You can contact your purchased Theme Author because Item Author are best expert about their Item functionality.