Further testing yielded the following:
I’ve used Octoprint on my 3D printer for a couple of years and was interested to see a laser plugin for it. I added the Laser plugin to Octoprint on my laser engraver and like what I see - with an exception. I was seeing artifacts in a photo I was test-printing, then saw more definite lines when printing a gradient image. I went through steps of eliminating different parts of the communication path to determine the item causing the issue.
My system consists of an RPi3 feeding an Arduino/BOB unit to drive the steppers and a laser driver module to operate the laser itself. I bypassed the RPi to start with and got smooth prints. Then, I set up two SD cards - one with Octoprint Laser and one with bCNC to further drill into the cause. It turns out that the print discrepancy only occurs when using Octoprint Laser to feed the gcode to the system. Attached is a photo showing the result using Octoprint Laser on the left and bCNC on the right.
Bottom line: Running the gcode generated by LightBurn using the RPi/bCNC feeding my laser provided a smooth image, as does bypassing the RPi and running the laser directly from LightBurn on my PC.