[Solved] Terrible prints on a Prusa- assembled MK3S+  

Terrible prints on a Prusa- assembled MK3S+

I bought an assembled MK3S+ that arrived yesterday. Out of the box it's printing terribly. There are layer inconsistencies along the X-axis, as seen in the below image. The Y-axis sides of the cube are perfect. Only the X-axis sides have the issue. I have an older MK3S as well, which prints great.

So far I have run the XYZ calibration and 1st layer calibration. I've also checked the belts with the Prusa tension meter ( https://www.prusaprinters.org/prints/46639-tension-meter-for-the-gt2-belts-of-i3-mk3s-or-prus) that was properly printed. The X-axis belt was very loose, so I tightened it to specification of the meter. In the picture below you can see a small improvement after the calibration and belt tension adjustment. 

Any other ideas? I'll reach out to support after the holiday if I'm unable to resolve the issue by then. The test cubes are printed with PolyMaker PolyTerra PLA.