why the maintenance page is showing “sign in to access this site”

Like the Topic title says …why the maintenance page is showing the “Sign in to access this site” window instead of the maintenance page?
In some other browsers, it showed the normal web page with its templates, pages, etc like if it is not in Maintenace mode.
I have tried purging the cache in Siteground that is the web hosting provider and cleaning the Google Chrome, Microsoft Edge, etc and nothing has worked.
I also have tried disabling and enabling the plugin and making any little change to save it and to reactivate it and it has not worked either.
Can anybody help me?

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