Thank you for the donation!
That said, that is a very strange interaction, and I am afraid it may not be something we'll able to fix. Despite being intended for use with a drawing tablet, Spud Tablet is based entirely on cursor tracking, and not on anything tablet/pen specific. It appears that Windows Ink is preventing tablet/pen input from moving the cursor while it's actively drawing, so the arm doesn't move because the cursor isn't moving.
I'll see if I can figure out some way to work around that, but I can't promise I'll actually be able to come up with anything, sorry.