One of my props is not like the others. I can free spin 3 of my props down, they bottom out, then I hold the motor and hand snug the prop, maybe getting a 1/4 inch(ish) of tightening before they're as tight as they are getting. One of my props (black) free spins, stops, then I can hold the motor and get three or more full rotations of tightening and never bottoms out like the other three.

I contacted DJI through Live Chat and got an immediate reply asking for a video. I sent the video and am now waiting for a reply.

By the way, none of my "spare set" of props have that problem.

I have gotten a few shipped to me for my phantom like that threw it away...Wouldn't thread.

I have the same issue (almost), however, it's one of the motors that doesn't seat the props like the other three.  But in my case, the props will seat tightly.  I tried other props and get the same result, so it's likely the motor on mine.

wow not good. Mike

DJI Customer Support sent me an email requesting Serial Number, Purcahsing Agent, etc.

DJI's Chat Support has been accessible and communicated in a timely manor.

could this be one of the reasons props are coming off in flight?

i had the exact same thing, when i first got it all 4 would tighten down nicely with a flick then a hand tighten to check, few flights ago i noticed it went tight 3/4's down and i now have to hold the motor while doing about 4 more turns. It is also a black prop aswell