Zyxel atp 500 very high CPU level

I have a Zyxel ATP-500 at my company. For about a month now, the CPU usage has been stuck at a high 90-99% as traffic increases. This prevents anyone connected to the VPN from working, and the internal LAN has been performing poorly. Where can I start checking to see what's causing the CPU usage to increase? Last Firmware. I have active:

Web Filtering, AppPatrol,SecuReporter,Sandboxing,Reputation Filter,Collaborative Detection & Response,Application Security,Intrusion Prevention.

Thanks for your help