Hi @waf - there maybe some slight variations in the arm being parallel to the surface but the thickness of the sponge should be able to absorb that. The spring in the pen is also designed to absorb any differences over the surface. We would recommend putting the drawing settings back to the settings that were working before.
If your board was operating fine before, unless it’s taken a knock or something has come loose, then it should be well with operating tolerances. Could you give the moving arm a gentle wiggle and see if there’s any unexpected movement? Can you see the sponge pressing fully across the surface when the wiper bar engages?
If you wipe the surface with quite light pressure with a micro fibre cloth - does it remove the ink easily or does it require some pressure to remove? It might be that the surface needs a good polish as dried on ink will cause further jots to stick.