The screw wasn't impact damage. If it's a screw going into metal, you must use loctite on it. Don't get loctite on anything plastic though as it will weaken it.

And yes, if your Debonair was built according to the original plan it does have bad stall characteristics. The leading edge is too sharp and the top of the airfoil isn't rounded so you are going to get a snappy plane. Switching to the "RNAF" wing design will help some, but the sharp leading edge will still keep it from flying as gently as a standard balsa trainer.