BLOX User Accounts are typically limited to one login at a time. This is intended to reduce account sharing.  However, by going to Settings / Users / Authentication, you are able to allow your users to have Concurrent logins.

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Clicking the Enabled box will turn on the ability for users to be logged into your site from more than one device using the same username and password.  After the Enabled box is checked, enter the number of concurrent logins any one user can have into the Login slots per user field.

In the next area you can determine what happens when the user reaches their maximum number of login slots.  If the first (default) option is selected, the oldest login will be forced closed when a new login is attempted.  If the second option is selected, the oldest login will only be forced closed if the maximum 'age' has been exceeded.  If it has not been, then the new login attempt will be denied.

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Beginning in BLOX 1.18.2, if you exceed the maximum number of login slots in the same browser, the oldest login in that browser will be recycled first, even if there is an older login in a different browser. Also, different version numbers of the same browser will be treated as different browsers.