Logout forever

I bought this (premium) plugin a couple of years ago. Since the last update, despite trying to uninstall and reinstall the browser, delete cookies and cache, renew the main theme (X of the theme.co), deactivate ALL the other plugins, I discovered today that the cause of the continuous logout was WP FASTEST CACHE ??

I tried in every way, choosing the best options, deactivating them all but the plugin, after a few seconds of navigation, forces me to logout.

The page I need help with: [log in to see the link]