@TGFNM14
I tried some guitar holds that essentially pinch the lower bout between the right thigh and upper right arm to hold it and doing that resulted in the flying neck syndrome you describe, in spite of my lack of a half beach ball.
My guess is that you aren’t adjusting the strap to hold it well enough, but I dislike straps.
What worked for me was to get a lift like for a classical guitar and play in the classical position with the guitar supported on the left leg by the lift. I did this before I started classical guitar and even bought a lift for my electric guitar. It is much more secure that way and the neck stays put.
Try rolling a towel up into a 4-5” wrap, secured with several rubber bands (to hold it and to keep the guitar from sliding. Put it between the waist of the guitar and your left leg and adjust it around. If that seems to be a good position for you, look into more secure lifts.