Some other “long shots”.
If you haven’t already, try getting support from Wacom. I have found their support “less than optimal” but you never know!
I don’t know the Cintiq at all but my Intuos Pro has small slider on the side which turns “touch” on and off. Using it seems to cause unpredictable results, one of which in my experience, is causing the pen to make marks without the pen touching the tablet. If you have such a slider try giving it a slide. There is also on my tablet in the pen settings (from the Wacom desktop) an option called ‘hover”, turning this on and off also can cause weirdness.
As last resort there an app called “connect my tablet’. It costs $NZ 20. It’s very good for failed or misbehaving Wacom installs. It has helped me but YMMV
Kia kaha
Brett
"You do not suffer because things are impermanent. You suffer because things are impermanent and you think they are permanent." ~ Thich Nhat Hanh
Tech stuff: 24" iMac M1: Wacom Intuos Pro L: iPad Pro 12.9"