Records are not inserted

I have created a new user registration form.  Before giving new users privileges, they need approving first.  I have created a waiting authorization table and a users table to handle this job. 

At times, I am experiencing that selected user(s) are not transferred to the users table from the waiting authorization table and several attempts are needed.  Does anyone have any ideas as to why this is happening?

I am using a mySql database and PHP.