It is weird that your team can't reproduce it. I'll try to explain more. It seems that in exp 1.3 has more agressive controller sensitivity curve than in stable. It might be happening because added inertia or some other setting interfering cyclic controls. I added picture to show what I mean.

Because of that it makes almost impossible to keep stable movement while turning because there is no middle ground anymore - you either have too little or too much input thus effectively making it more like keyboard input not analog as it supposed to be. This new flight model is realistic only to the fixed wing aircraft, rotary wing should have more sensitivity for micro adjustments as it is in stable 1.2.1 (it isn't ideal but much better than in 1.3 exp). I've added youtube link to comparison video that I made. It should explain more what I mean, you can clearly see that in exp 1.3 flight model makes me jank my sticks because it either gives too much or too little analog input while in stable I can fly pretty smoothly.