If you have a situation where a vector doesn't close, especially with circles, you can help mitigate that by turning on the 'Hide Backlash' feature in the Optimization Settings in Lightburn. This is what the developer says:
You can find the official LightBurn Documentation here:
https://lightburnsoftware.github.io/NewDocs/OptimizationSettings.html#hide-backlash
NOTE: This setting alter is the motion planning in a way that is not as efficient most times. and it disables a few of the other optimization settings when its enabled. so i would leave it off unless it happens to be needed:
Here is how to turn on 'hide backlash' in the optimization settings in lightburn