These are jumpy little pistols and some of the problem may be that the shooter's thumb position hits the mag release upon recoil. Changing one's grip to keep the thumb from resting right up against the release my help. My LCP II had a very stiff mag release spring. When new, I had to depress the release to insert the magazine. It has since broken-in such that the magazine readily inserts as expected. I've never had a issue with the magazine coming out under recoil. I just took my LCP II out and yanked down real hard on the magazine trying to get it to release without pressing the release and couldn't do it. One would expect that if the recoil alone releases the magazine, one should be able to yank it out of there.
My two-handed grip on the LCP II: I grip it with my right hand with two fingers under the trigger guard and my pinkie under the magazine. With my thumb on my right hand held out, I then grip the pistol with my left hand, with my left index finger falling between the middle finger and ring finger of my right hand and my middle finger of my left hand falling between the ring finger and pinkie of my right hand. The last two fingers of my left hand rest under my right hand. The thumb of my left hand rests along the side of the middle finger of my right hand. The thumb of my right hand rests over the top of my left thumb, between the thumb joints. Neither thumb touches the left side of the pistol. The thumbs form a nice triangle shaped pocket around the mag release. With this grip, I've never had an issue. One fellow on You Tube who was accidentally releasing the magazine upon recoil added Talon grips and got enough friction to keep his thumb in the grip indentation, keeping it from falling down and hitting the mag release. Either way, I think changing the grip, being aware of your thumb placement, will correct many (but not all) of these mag release issues with these little pistols.