I think you might want to double check your ph pen is accurate, recalibrate it. Then do a small flush and a light feeding. Fortunately you're so close to harvest it probably won't matter with this plants success, but you don't want things continued into the next grow.
I recalibrated my ph pen the other day and somehow it was a whole point off...whether from extended often use, or the pens just wear out over time.π