I have a LultzBot TAZ 6 3D printer and the software I use for my prints is "Cura LulzBot Edition - 3.6.3". All of my printing settings/parameters are at their defaults (i.e. no personal customization is employed).
Below, two pictures are included that highlight an issue I have observed in many of my prints; these prints are carried out using the "default settings" provided by Cura for PLA. The two pictures are different orientations of the same printed out object; the volume of interest is outlined in red. Additionally, this volume represents the first several layers that are laid down by the extruder.
I am not familiar enough with 3D printing jargon to know if this has a particular name, but as you can see, there is clearly a lack of homogeneity in the laying down of several consecutive layers. Depending on the object being printed, this is not necessarily an issue. However, some of my objects have features that occur near the first several layers and are therefore affected by this issue.
Additionally, some of the these objects are inserted into other pieces, which are designed to be very tight-fitting. If you look carefully, you will see that this lack of homogeneity in the layer deposition leads to bulging of the PLA, which can increase the thickness of the part by ~0.5 - 1.00 mm for several layers. This increased thickness prevents these insertion pieces from fitting into their appropriate locations.
Any suggestions for fixing this issue? Is it an issue of over-extrusion for the first layer that then propagates for a few additional layers? Remember, all settings are at their software defaults for PLA.