Rick thanks for your feedback.
I upgraded to version 9.02 and the status is the same.
The initial file was created in https://www.makercase.com/ and the resulting file Box.dxf was uploaded into LightBurn and modified.
It was saved a couple of times before the lock/loop happened.
The file is available to study it, or to use it as a debugging test demo or error seeking.
The more intriguing issue is the circle with arrows in the upper left corner, do you have an idea of what is the meaning? Also the “nan” in the location/dimensions numbers.
Sorry for my English, it is not my first language.