Membership sign-up inconsistencies

Hi,
The biggest problem we are having now is the membership signup is inconsistant. When I run tests and sign up for memberships everything works fine. I'm added as the correct member in the dashboard and I'm automatically added to recurring billing. But whenever someone else goes to register it hasn't been working. It puts their username in the system, and authorize.net accepts payment, but it doesn't put which membership they signed up for, add them to recurring billing or even send the new member notification ping. This problem is becoming a big issue because we are having a hard time determining what people sign up for due to a current promotion.

Thanks,