I have the 4 meter version of this plane and the few times I've flown it, I have never experienced a tip stall. I agree with Joo, you probably have a bit of washin, instead of the proper washout. I am not too sure about the CG thing, because I find most European planes in this size range, 3 to 5 meters, with the CG already set too forward.
You should assemble the plane and look at it from the winglet or tip and see if the angle decreases from the wingroot to the tip, in fact the tip maybe angled slightly down in relation to the wingroot. But if you see that the tips are angled higher or the same relative to the root, you probably got a problem but it's fixable. Also be aware, that one wing maybe perfectly fine and the other, the one you turned into, may have the washin problem.