It appears you have greatly enlarged the vertical fin area.

While there is no down side for enlarging the horizontal tail area, the vertical area should be kept between certain limits. Too small and you get into yaw instability. Too large and the plane gets into spiral instability. The normal size of the total vertical area is from 1/3 to 1/2 the horizontal area. ( Horz area normally 20%-25% of wing area)

What happens in spiral instability is the plane tends to tighten up a turn or spiral. When you roll into a bank and pull back, the angle of bank will tend to increase as you go around the turn. In a diving spiral, the spiral will tighten up and you probably not be able to pull the nose up until you roll out of the bank.

You probably recall flying a friend's trainer that tries to roll out of the bank during the turn and you have to "touch up" the aileron as you go around. Same thing here except you touch some top aileron to roll out a little during the turn.

It's nothing violent and I have encountered it before in a couple of my designs. It's just not a comfortable way to fly. It would be nice to know if you do encounter spiral instability.