I am relatively new to Lightburn (on macOS). I’m running a Comgrow 5W laser on a Creality Ender 3 Pro 3D printer on Marlin.
When I use the fill setting on text, I have multiple stray lines appearing on the outside and unburned lines in the text (see picture). I use a relatively low speed (1000 mm/min).
Updated versions can be an improvement, but it really depends on the settings the firmware was compiled with. That thread has a post on March 14th, (post #10) where he mentions the changes he had to make to the firmware to fix it.
Basically, the default settings for Marlin only update the PWM output for ten times per second, and it needs to be more like 1000 times per second in order for it to work for laser use.