You do not say whether you had fitted wing fences and the dorsal fins beneath the fuselage? On the full size the surface area in front of and behind the CG is meant to be in exact balance. On the military version the addition of armament surface area had to be balanced by additional surface area at the back. The handling was then unaffected. My view is that wing fences. preferably somewhat larger than scale are an important anti-tiipstall device.

Murphy's law, of course, predicts that you had carefully fitted them, whereas Ali, who has had no trouble, did not!

Can you recall whether the disasters took place at the beginning, middle or end of the flight and where you had the CG? The fuel load can move the CG somewhat.