I went through this awhile back with my prop-hubs. I noticed that some were loose, but when I went to tighten the screws, they were already tight. So, I removed and re-seated the screws, and this tightened everything up for a flight or two, and then, the same hubs were loose once again. I could only conclude that the fastener holes on the plastic hubs 'wowed out' (or opened up a bit) around the three fasteners, and as such, I replaced all four of the hubs and assorted hardware with the original, stock versions that I ordered.
Then, enter DJI's new version of prop-hubs for the P4. They eliminate the metal plate with the three finger-springs that are so prone to being bent downward after use, and rather, there is a single coil-spring that slips over the motor shaft, and then, the plastic hub goes on over it. They are a much tighter and more secure fit for the props in my opinion. But, more than that, if you take one of your old-style prop-hubs and plates off with a 1.5 MM hex drive, you will see that there are holes in the top of the motor housing other than the three fastener holes. The newer style hubs have two tabs at their bases that plug into these holes, unlike the original style hubs. In theory then, with this new design, these new hubs should be more resistant to the fastener holes 'wowing out' around the screws because of the torque of the motors since they would be more resistant to slipping sideways under power, especially at startup or during braking.
The key is to tighten them until tight and then a tiny bit more. Any more could strip out the threads in the motor housing, and any less could allow for slipping which could shear off the tabs, and then, who knows.....