I have a zonestar P802QR2 model. This problem has been appearing since I first started using it and I'd really appreciate some help here!
The prints always come out wavy and I'm guessing the y-axis is the main problem since the wavy lines come out stronger when moving in certain directions. The worst is when its moving towards the +ve y-direction.
I printed an octagon outline here to show the difference for different directions. The problem appears regardless of the speed setting. (ignore the poor taping, it doesn't affect the current problem)