Don't want to be an alarmist but following a repair (where most of the time DJI sends a new/refurbed unit) I had the same problem that the props were really hard to get on. On about the 6th or 7th mission the drone was coming in for a landing and about 50 feet it shed a prop and crashed. Was able to recover the prop that came off and it still had the plastic clip mounted on the motor, and one of the screws that holds the plastic clip on top of the motor. The screw did not appear to be stripped and it did still have evidence of locktite on it. I couldn't tell if the motor screw holes (where the plastic clip is held to the motor) were stripped. I'm convinced that it was a tolerance issue and the fact I had to use a lot of force to engage the props to the clips was responsible for the failure of the screw/motor interface. Personally, I believe the tolerance issue is in the props and not the motor/clip. Hope this helps.
The v2 P4P is known for this problem. Some have even drilled the props deeper to fit. I would suggest replacing with DJI P4P prop mounts from Amazon $10. They Fit! From the v1 so they are not too tight. Good luck.
I noticed mine were difficult when I first got it, but after a little (gentle) trial and error, I realized it was more just a question of technique. Push down too far, they won't click into place. Don't push down far enough, same thing. Remembering which ones turn which way is helpful, too. After some practice, the Phantom and I get along just fine.
The drill route was my solution. Removed some material from the hub where the motor shaft bottoms out. I’m pretty much convinced this relates to something being changed in the motor shaft/bell housing assembly process. Some dimension has changed.