Your results are symptomatic of a backlash problem, a common hardware issue. In LightBurn, Optimization Settings, you can enable ‘Hide Backlash’, if the problem with the circles improves significantly then you definitely have a backlash issue.
I have attached a small program called backlash test I have just made, which should provide an easy method to help you identify and measure backlash.BacklashTest.lbrn2 (166.1 KB)
Turn off Optimize cut path and run the program, it should start where it says start, if you measure with calipers the gaps a,b,c,d they should all be the same. X backlash will result in slightly greater b gap, and Y backlash greater d gap. With the top section I made the gaps small so it might be easier to visibly see a difference.
It is always better to identify the source of backlash and to eliminate it so that the “Hide Backlash” setting is not required. As well as checking your belt tension you should check your entire drive-train to make sure there are no places where there is “play”, check the grub screws, shaft couplings, drive pulleys etc.
It’s hard to describe but while the motors are powered on and holding position it is possible to push and pull on various parts of the drive train to look for any looseness/sloppiness or (click for example)movement where there shouldn’t be.
After you have done all you can to mechanically eliminate backlash, it may also be possible with some motion controllers to enter a backlash amount for each axis and the controller will attempt to automatically compensate.