I don’t know why but my prints with creality 5.x.x. suddenly get ribs (lines of the mesh on the outside) the surface is not smooth as it should be.
I have the latest update creality slicer.
There could be a few mitigating factors, which version of CPrint are you using? Some versions work better than others, some are just painful to use. Creality has a repository of older versions.
Could you post a pic of the issue?
Do the “ribs” correspond to your infill pattern?
These are a few options that may contribute (V5.1.1.9490)