I wouldn't chance another flight with cracked props! Twenty-six dollars for a new set of props vs several hundred dollars for a replacement drone? C'mon!
I agree with what has already been said about the potential causes of the mis-shaped threads inside the black-dotted props - either the motor shaft is pressing against the interior of the prop hub cup or the threads themselves are not properly formed and cannot hold up under normal hand-pressure tightening.
If it were me I would let the vendor know what problems you are having - they may be willing to send you a new set of props just to keep your business.
Also, if you decide to throw these props away you might want to entertain the idea of cutting one in half - right through the middle of the prop hub along a line perpendicular to the extreme tips of each prop blade. A Dremel tool with a cut-off blade on it would work nicely (at low rpm so as to not melt the prop material any more than you have to to make the cut). If a Dremel tool is not available you might try an extremely narrow kerf saw to do the same thing - or possibly a razor knife.
Once you have cut the prop into two pieces you should be able to see the interior structure of the tip of the prop hub. Other than the material that is needed to make the prop hub wall itself, it should not have prop material between the bottom of the molded thread area and the beginning of the interior curvature of the tapered prop hub tip. If there is any such material, and if the end of your motor shaft is hitting that material (as Steve 7777 alluded to above) then you have a good case to claim poor workmanship on the part of the manufacturer.
