Mk Carbanti III drop rates

Has anyone done recent tracking on Mk Carbanti III drop rates from STR challenge? I use to regularly get 4-5 a drop, but the last few weeks(6-9 total days, 30-45 challenges) I've rarely seen a drop of 5. I understand RNG, but approaching 50 samples and rarely seeing a 5 is a tad odd. Just hoping I'm hitting a string of really bad luck.