Any luck?
I found out that the hinges AND the gas shocks on my 1 month old OMTech were loose, and that SLIGHT amount of movement was enough to throw my calibration off, to where it was never the same twice!
It seemed like every time I did anything (cut something, opened or closed the lid, turned off the power, etc) it would cause the image to shift in both X & Y directions, just slightly… but enough to be annoying as hell and make the overlay feature USELESS.
BUT… once I tightened up the shocks and hinges it improved a TON!
Then I moved on to my camera mount.
I mounted my camera to the underside of my lidand I was using a goPro/“linkage” style mount that I bought off Amazon (my camera has a 1/4" threaded nut for tripod mounting), but because of the mounts overall length, it acted like a “lever” and the weight of the camera would cause it to bounce any time I closed the lid, or I opened it up to it’s stops, and this slight amount of wiggle/bounce was JUST enough to cause the camera to shift on it’s plastic bushing, resulting in the bed image shifting by 2mm or more! (I couldn’t detect any movement when I tried by hand either… it looked/felt SOLID when I pushed on it with a finger).
So I replaced the long center “stalk” of the mount with a much shorter version that I 3D printed, and this resulted in the camera sitting much closer to the lid of the machine, eliminating the “lever” effect.
I also replaced the cheap, plastic, knobs on the camera mount with regular nuts and bolts, which allowed me to CRANK them down (after I got the alignment just right), further eliminating movement in the camera when moving the lid.
The final (and most dramatic) step that I took was once I had the camera position nailed down EXACTLY how I wanted it, and I had the bolts cranked down as tight as I could get them without cracking anything… I used the laser to cut a cube of foam down to the perfect size so that I could wedge it back behind the camera so it would give the camera a surface to rest against, and provide a slight amount of resistance against the tightened camera mount.
Then I rolled out a “worm” of modeling clay and wrapped it around the edge of the camera where it made contact with foam block and I gently worked it into and around the junction, effectively “sticking” the camera up against a backstop, COMPLETELY eliminating any sort of residual bouncing or flexing that the camera had in it’s (now rigid) mounting setup.
Even when I close the lid a bit rougher than normal, the video output doesn’t “bounce” when the lid hits the bump stops, the moving image just “stops” dead, with no rebound or bouncing visible at ALL.
After all of this, I no longer have any issues with inconsistent overlay positioning except for the rare occasion when I accidentally whack the camera with a piece of material that I’m loading/unloading, or… when I bump into it with the back of my head after I stick my head into the machine for various (probably irresponsible) reasons. 
Now the only camera-related issues that I have left are frequent contrast issues that are caused by the camera getting “blown out” by the LED strips that I installed reflecting off of white/light colored surfaces. And I also have a TON of problems whenever I switch my lens tube to a longer or shorter tube (to change to a different focal length for cutting VS engraving), it changes the distance between the camera lens, and the bed, and this throws my entire lens calibration out of whack, nothing on screen is straight or square.
I wish Lightburn would either allow multiple camera calibrations to be stored, or they would incorporate some sort of fixed calibration pattern (stickers maybe) that you just stick onto the border of the bed so that the software could do some sort of automatic calibration before every job (or on demand) so it could automatically compensate for lens distortion due to changes in Z height.
Oh well, one step at a time!
Good luck mate!
-Dom