There are many many other things to check when looking for backlash:
- Bad factory assembly
- Loose focus lens or mirrors
- Loose screws anywhere
With the power off, push the laser head by hand to feel for loose motion, then track it down and fix it.
Also, turn off LightBurn’s Hide Backlash switch and make sure the controller’s Backlash settings are zero. The only way to fix mechanical backlash is to fix it, but it’s also possible to have the software introduce backlash by “hiding” it when there’s nothing to hide. 
Fixing the backlash may also cure the ragged engraving edges, but if not you should measure and set the Scanning Offset Adjustment table:
Good hunting!