Offset start/stop points intermittent

I was having trouble calibrating my machine the other day (shenui 350 50w blue and white) and I thought that I would run a test of circles and ellipses to see how bad it was. I noticed a weird behavior in start/stop alignment. I then tested it in rdworks and had a different result.

I ran the same program in all 4 corners of the machine. I drew all the shapes inside their respective program. I used the same settings of 25mm/s cut and 20% power (~8mA). I cut on the same material.

First image is the test from all 4 corners in rdworks. The inside circles come together better. No changes to machine and hand drawn in each program.

Second post has the lightburn program. You can see that the smallest circles struggle to come together.

Bottom center in RDWorks looks similar. Top left inner circle is also very warped, even though the end points meet, so it’s likely that RDWorks has “backlash optim repay” turned on, whereas LightBurn doesn’t have that. It changes the direction of cutting order a little so the head tries to keep moving in the same direction to minimize the effect of backlash. Yours looks bad enough that it’s likely mechanical - loose belts, pinions, or couplers on your Y axis.