Monoprice Maker Select V2 - Missing Layers

Hi guys, got about 5 days of print time on my Monoprice and I'm totally in love. Dialed in acceleration and jerk pretty fast, printed the diicooler for more uniform cooling, and more or less know the likes/dislikes of my different PLAs depending on print.
But I've recently been struggling with missing layers. They will either appear very regularly at distinct intervals, or only at the tops of some geometry. Any idea what could be causing this? Didn't find any clogs, tried slowing the prints down to 40 from 60 mm/s and even upped my flow to 107%.

10mm³ Test printed at .2mm layer height, 210 degrees, 90% fan speed, 40 mm/s: http://imgur.com/a/K1EHu

Any input you have would be great, thanks!


EDIT: Solved! The issue was a small amount of old filament that had shaved itself off of the extruder and wound around the axle, causing cyclical issues in feeding.

Printed again at 1.2mm Layer Height, the missing layers are still there at regular intervals, but much less apparent. Block now appears ribbed. http://imgur.com/a/map2f

EDIT: Tried changing Filament diameter from 1.75mm to 1.70mm to account for possible filament inconsistency. At .2mm layer height, 210 degrees, 40 mm/s there's virtually no change in missing layers. It HAS, however, exascerbated missing lines in the raft, as seen here: http://imgur.com/a/PUwGG