I had something similar happen on a built plane I got at a swap meet. Everything looked fine, and I got a few flights on it, until one day I had control issues and fought with it until it finally lost enough altitude and crashed. Turned out the push rod to the rudder came apart, but deep inside the fuse where it was impossible to see.

So if the push rod is a multiple piece one, like hollow tube with two piece ends, check them well and secure them even better if you can.

If the place were closer in, I might have been able to tell it was the rudder that wasnt working and I might have been able to get better control over it and had less damage done. Of course had I not OVERPOWERED the plane with a DLE20, it might not have come loose either. Even a 91 FS is too much for it, I think a 70 FS might be the right size. It is a big plane, but a slow flyer, with a huge wing. Size is deceiving.