Have you tested youre File on the SD Card and running from the mpcnc itselfs? With my old Notebook the USB Connection failure some Times and the Job aborted. What you can Test ist that you make a Job with estlecam starting the laser manuell and Run the Job, cryptobel phrases and letters in Lightburn were Made when you using a cracked Version from lightburn.
According to a post on this forum, Marlin has the bug fixed. The next time V1 makes a new release of their maintained Marlin firmware, the fix will be incorporated. The laser will then stay on if triggered from a Marlin-driven menu.
My solution (until the bug is fixed) is to manipulate the pin directly, rather than to use Marlin’s laser/spindle commands. See M42 for directly manipulating pins. Another way to get around the bug is to created a script where the laser is turned on, and then the script moves the spindle very slowly for a period of time, and finally turns the laser off.
Another solution is to edit and recompile the firmware so the laser stays on longer when not moving. This is not the best solution for safety reasons, but the line to manipulate is in configuration_adv.h: