It's likely because this has nothing to do with the cursor movement or interpretation of keystrokes by software, but something to do with USB/HID. You won't see the issue (or the solution to your issue) until you exercise something on the bus itself - which could also include BlueTooth.

If you have any software that accesses some other USB device, try sending some traffic over an endpoint to see if you get the same results.
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Bruno
Twisted Melon : Fine Mac OS Software