First - like the work! zbrush?
As to the issue: I wish I knew. Honestly, I see this on a lot of my prints. But since I'm not concerned with aesthetics, I've never bothered to sort it out.
Here are just a couple of ideas:
1. Supports not rigid enough for certain layers, allowing the already built model to shift slightly. The tray rotation used to separate the layers may make this worse as the model is alway seeing lateral forces. It may be that for some layers the model moves with the rotation and doesn't make it back into position for the next layers.
2. Z height position accuracy. If for whatever reason, there is an inaccuracy in the Z height, this would cause lines. I see wave patterns in my layer thicknesses from time to time. I usually attribute this to large cross section areas with incorrect wait times. No proof though...
3. Power surges or drains. If the power spikes of drops during a print, I would imagine the LED power could be affected. I don't know to what extent this is handled internally on the Ember. If this is the case, it would mean we should hook up our Embers to a UPS with power conditioning.