Some things you can look at
- Belt end needs to rotate freely on the anchor
- Anchor block must not move, secure it down tightly
- You are running two different versions of index.html.gz and firmware.bin. They should match.
Serial Messages
Index.html Version: v1.21
[MSG:INFO: FluidNC v1.20] - Floating control board is not a problem, but have a look through the printed parts thread for a couple of solutions which seperate the control board from the router.
Maslow 4 3D printed parts thread - The gap between arms is not generally a problem, putting anything in there may be counterproductive as it may restrict rotation,