Help - Scroeder CB-9" tonearm - anti-skating setting issue

Hope someone can help here.
I have an old (original) version of the CB 9" arm which was developed for the Artemis TT.

I acquired it recently after building up the whole Artemis system.

The issue I am facing is that I am struggling to set the ant-skating correctly.
I reduced it so far that the screw is almost falling out, yet the tonearm swings outwards as I am trying to adjust the cartridge using a Dr Feickert rig. Correct VTA/VTF set, using a Fidelity Research FR-1 MK III retyped by Soundsmith.
I can listen to the first 2-3 recordings on the record (so at least I know everything is working fine) but then it starts jumping back (like there is a skip in the record). Tried several records, same result.

Manu al very basic and could not find other posts anywhere.
Thanks in advance!
Laz