I have found the White Widow autos I grow really put up a fight at the end of flower (i know yours is a different strain, but...) and haven’t been able to put my finger on what it wants. I’ve raised and lowered my nutes and still end up watching the pH bounce around. I believe it’s just a sign that it’s done. Drinks water...choosy about nutes...and pukes pH up and down...i think next time my WW auto does that, I’m just going to flush-n-cut the harvest.
the chart below is a good thing to keep handy. Check your ppm/EC and see where you land on that chart.