Individual contributions on our site are working find but ARB transactions stopped working in March of 2016. Nothing has changed on our end as far as I know. I've upgraded to the latest Civicrm for Wordpress (v4.7.10), verified our silent post URL is correct at authorize.net, checked the API Access Key and Transaction Key are correct.
For recurring transactions, the initial transaction is processed fine by Authorize.net but an ARB subscription isn't configured and the transaction remains pending in CiviCRM.
I reached out to authorize.net and they stated they have no logs to assist troubleshooting and everything must be reviewed on our end.
Any ideas on where to check? We've got everything setup according to https://wiki.civicrm.org/confluence/display/CRMDOC/Authorize.net+Configuration
Only change I've done is to try the Akamai URLs rather than the older URLs.