I’ve played with screw/belt tightness but the result is Identical.
After I’ve activated Scanning Offset and played with different Values I’ve found that 1.10mm offset fixed the issue when Bi-Directional Fill is Enabled. However, I think that the 1.10mm value is pretty high.
I only have 10 days left to return the device so I would like to test and try to fix anything before making a decision.
That’s the likely source of the backlash. Carefully align the gear such that the grub screw can be secured against the flat of the shaft. There may be another screw adjacent to that one that should also be secured.
It’s a mechanical issue. Go through this guide to set up your mechanics correctly: Guide to mechanical adjustments and maintenance The laser is not tuned from the factory, you need to check every bolt and screw to get great results.