A Concrete CMS package to prevent each user has more than one active session simultaneously.
Just install this pacakge, then it will automatically invalidate sessions except the most recent one.
If you can't sign in to the CMS after installing this package, you can uninstall this pacakge from cli interface. See: https://documentation.concretecms.org/developers/framework/console-commands-and-jobs/command-line-interface-cli-commands#c5-package-uninstall