Hello @borrypsy,
The Restricted Access page is usually shown when the Login Access feature has been configured and admin access is allowed from specific IPs only. These settings can be adjusted from the WordPress Dashboard >> Security Optimiser >> Login security >> Login Access >> Configure. In order to access the site’s admin – you will need to do so from the IP which has been allowed within the above mentioned settings.
In case you’re unsure of the IP – you can proceed with re-installing the plugin a new. You can uninstall the plugin using wp-cli or by deleting the plugin’s folder. In case you remove the plugin manually by deleting the folder, make sure to remove all the tables generated by the plugin, as well as any plugin associated entries in the _options table – cron scheduler, version definition (sgs_install_xxx), etc.
If the issue is still present after reinstall and if you’re a SiteGround customer – you’re more than welcome to contact our Support team so we can further review the case on your behalf.
Best Regards,
Gergana Petrova