Symptoms should sound very familiar to y'all: Windows 10 as a guest and the mouse pointer not tracking properly; always offset by some amount making it hard to reach anything on the edges of the screen.
I tried setting usb=1 and usbdevice=['tablet'] but it only sometimes helps. Multiple reboots seems to make it go away, but it always comes back. In one instance, I had 5 reboots in a row before i could get it working again.
Going into windows "Mouse Properties" and unchecking the "Enhance pointer precision" ticky box only helped when I vnc in from my laptop and use a mouse. I'm running vnc on a touch screen (only; no mouse or keyboard) monitor and so this workaround doesn't help me.
And indeed, the "Intel 82371SB PCI to USB Universal Host Controller" is not initializing correctly; it has the yellow warning triangle on it. When I remove it (right click, uninstall) and rescan, my mouse works correctly again.
Unfortunately, this is intended to be a kiosk, and it needs to be reliable. I can't ask someone to check on it every time it reboots, and then go into the back to fiddle with the server (most people won't even have access to the server). Plus, it's not like I can remotely detect that this is a problem, and just automatically reboot until it goes away.