It is not a shift. It has to do with the fact that the bottom is pretty solid and the walls are not. They contract and shrink differently due to cooling and that is what comes out as the lines around the bottom.
The poor quality of the bottom where the support interfaces with the box is a result of the fact that the slicer is leaving some space between the top of the support and the first layer of the product. If the slicer would not do this the support would never come of the product. There are some ways to mitigate this by using PETG as support interface layer for instance, but that is pretty advanced.
For an out of the box printer with standard settings your printer is doing great!.
Cheers!