Odding

Hi, I am using Affinity Designer on iPad Pro 12.9 inch (2018.10) + Apple Pencil 2, both iOS and the app are up to date, for some reason the vector brush tool won't work with pressure sensitivity. It's always fixed width no matter which brush I selected, and when I tried to adjust the pressure by dragging the pressure handles, it always came back to default settings. Could anyone help me with this issue? Thanks! O.