Try these fixes for your Surface Pro 6 pen jumping in OneNote:

1. Check "Ignore touch input when using pen" — Go to Settings > Devices > Pen & Windows Ink and enable this. Updates sometimes turn it off (Reddit).

2. Replace the pen battery — Intermittent behavior is often a dying AAAA battery.

3. Re-pair Bluetooth — Remove pen from Bluetooth devices, restart Surface, re-pair.

4. Update drivers — Check Windows Update for Surface firmware/pen driver updates (Microsoft Support).

If it still jumps, try docking/undocking the pen to the Surface magnetic strip or use the eraser button to reset connection mid-session.