Repeating Payments with Authorize.net Problem
1) Make sure the Silent post URL is properly configured in Authorize.net.
Example: https://YOURSITE.COM/civicrm/payment/ipn/2 (the 2 needs to be replaced with your CiviCRM Payment Processor ID#)

2) It is possible that recurring payments are not processed instantly. It could be that recurring payments are processed in the middle of the night for example and therefore the payment will remain pending until it is processed.