I think you've discovered why cheap Chinese printers are so cheap :) Pretty much all of them have some design flaws, and there's always a certain amount of gamble with factory assembly and quality control.
This printer only has one z lead screw, right? It can be very difficult to get good contact with all 6 wheels and to completely eliminate gantry sag. If the vertical "legs" of the printer aren't at the perfect distance it might not even be possible, but sometimes it's possible to adjust them by loosening the screws, pushing the alu extrusions to one side, and tightening them again. If you're really unlucky the screw holes aren't drilled right and you'll never get good contact. This is an issue for all printers that have single lead screw + v-slot rollers. I spent a lot of time trying to fix this on my Ender before I gave up and bought a kit with a second lead screw.
IMO just try to do it as good as you can, perhaps you can get good contact for all wheels except 1 and then you can ignore that one.
Btw it's highly recommended that you print some bed cable strain reliefs for this printer, unless Tronxy has added this recently to the model. Otherwise the bed cables can snap