ARMember Plugin login goes wrong

I’m using ARMember Plugin to build a membership in my website, to allow people to log-in to a section where they can access exclusive content. Every now and then, the following problem occurs: when someone registers with their emails, or logs in, it sends them to the backend of WordPress, as if they were admins. Also, it sometimes won’t let the users log out.
Does anyone know if it’s a configuration problem? Or a redirection problem? Maybe an interference between plugins? Otherwise, what could be the cause?