I had a glider that did that too. It was a combination of slop and stiffness all in the cable and sleeve pushrod to the elevator.

The result was the same as what Scar described but from a different source. With the model on put in some up elevator and slowly return to neutral and see where neutral is with a ruler against the rear of the elevator. Do the same with down and slowly back to neutral. If there's any difference that's more than about 1/16 inch that may be your problem. It may be radio (dirty pots in the servos or even the transmitter sticks) or it may be the control system.

Beyond that try moving the balance forward a little and retrim the elevator. That should fix it. Where was the CG before it crashed?

Other than that I suspect Paul is right about the mechanical slipping thing. Sometimes the simple things bite you like a stripped thread in a nylon clevis that slips when you least expect... Yep, had that one too.