Why would a plant continue to grow new white pistil late flower

why would a plant grow new white pistil on top of matured bud? 12-14 weeks into flower
dwc 4 diff plants 4 diff times it has happened
I change the nute water out weekly (1to1 ratio)
one plant I increased the ppm the other plant I lowered ppm with the same result.
I have also decreased the light hours from 12 to 11 to 10 (different grows)
 
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