I have only had issues with it recently, but I know that a lot of people have been running into this issue with their prints. On the facebook group, someone posted that they had found a fix using Cura and Slic3r. He said that he was able to remedy the issue by switching the method for printing walls from what the Cetus3D software does, printing the inner layer first and then the outer layer, to what Cura and Slic3r give you the option to do, which is print the outer layer first and then the inner layer.
Some trial and error by users has suggested that it has something to do with infill, and that may be, but Ted at least found a work-around, moving the ridges to the inside of the print so we don't have blemishes on the outside.
Hopefully the Cetus3D team quickly switch the Cetus3D slicing procedure so we can see if it fixes the issue.