Cap 232 and it's "habbits"
I built a Great Planes Extra 300s 0.60 size and I have the same problem. I did the usual stuff like making sure the wing, stab, and rudder were all square. I took all the slop out of the split elevator linkage by using carbon fiber control rods. I mounted the elevator servo horizontally instead of vertically so that both elevator halves moved exactly the same amount. Checked the CG. I cranked in more right thrust. Still no improvement. Finally, I tightened up the ailerons by replacing the servos (wing has one servo per aileron) with ball bearing servos and I went to 4-40 control rods instead of 2-56 rods, and I used clevises at both ends to get a tight fit in the control horns. Also added some weight to the nose. These changes made noticeable improvements. Further research seems to show that the tapered, square tipped wing is prone to tip stalling if you push it too hard. That is what is happening when you pull up hard. There is no washout in these wings so they will fly the same upside down as right side up. My leading edges are pretty sharp so I am going to sand them down and see if that helps. I too was disappointed to find out that my aerobatic plane can't do a sharp loop but this snapping is also a characteristic of the full scale planes.