Please note, that the member count is based on active users. It seems the new user have not confirmed his/her password, and it's inactive. The inactive users cannot be displayed in the footer statistic. Go to Dashboard > Forums > Members admin page, and you'll see active and inactive users.
In case you want to say thank you !) We'd really appreciate and be thankful if you leave a good review on plugin page. This is the best way to say thank you to this project and support team.