I agree, it's probably velocity, and on one part of the layers the nozzle comes in from the left and on the other part if comes in from the right. I think it curves into or out of the model slightly where it may stop to extrude and 'coast' on the pressure in the nozzle to lay down the last part of the line. If the pressure drops, the line needs to move a bit outward since it's going to have less pressure and will lay down a thinner line towards the ridge in the piece.
Did you print the part and compare it to the preview? You can also wait and see while printing from which direction the nozzle comes in, or look at it in a different slicer like
http://gcode.ws/.
Edited 1 time(s). Last edit at 05/19/2019 02:37PM by Ohmarinus.
http://www.marinusdebeer.nl/