I tend to think that when these things happen to me it's just my "time of the month" ~ everything else can be consistent (hardware/software/technique) but your body/skin/environment you have little control over.
No, I won't get stroppy, hormonal, grumpy, teary, blah, blah during my "period".... but maybe my body is doing some self maintenance and expelling toxins through the skin creating micro acne or something similar. Maybe you've not had enough vitamins in the last few days and patches of skin are dried out as a consequence. Maybe the changing weather or humidity are bringing less natural oil to the surface of your skin, or maybe more (sebum).
Could be a microscopic small inconsistent rough surface on the blade too....
Maybe many things but at the end of the day it's all good, better getting a nick and a weeper than looking lazy and unkempt
