This happened to me twice. The first time it went away on it's own. This most recent time I had updated to 14.7.2, but also had my laptop fall off the couch, so I didn't know what it could have been. After seeing similar issues online, I figured it must be software related.
I updated to 15.2 (reluctantly!) and it's now fixed. I updated my computer the other day, and I did it with my computer connected to an external display and with the laptop closed, so I wonder if that might have contributed to this happening! It appears that the calibration process might happen during software updates, and maybe if your lid it closed while you update, the calibration process doesn't happen properly.