Command or Shift key modifiers always activated
I do experience the same issue. I have spent hours on debugging this issue. As I found it this issue exists for a long time. I don't sure about 6.3.32-4. Wacom support keeps recommending to reinstall the driver. I am also in contact for a RMA. I guess it is a driver issue. The shift click issue is reproducible using Wacom driver 6.3.35-2 and 6.3.36-2 on macOS 10.12 and MacOS 10.14.

Solution:
In my case I went back to Wacom driver 6.3.34-2, which resolves the issue.