When a feature changes on one part, it affects the print of the other part. I'm assuming that it's because it the start point changes on the second part depending on where the first part finished.

And while there are two parts, I get a wavy effect on the walls. When the first part finishes, the taller part continues without the wavy effect.

What causes these issues? Should I just print one part at a time? Or at least, print identical multiple parts?