Yep, the aircraft is snapping and can cause catastophic results if it occurs a low altitude. Cut down on your elevator throws until it will perorm a loop without snapping out. Adding exponential on your throws will help also.
Because the snap is essentially a tip stall it generally causes the most trouble if you have to add sudden power when at low altitude such as on landing. The airplane will tend to snap out and roll over onto its back ending in a crash.

Regards,
doubledee