With the writing-mode property value set to vertical-rl the end of the element in the inline direction is changed from right side to the bottom, and this also affects the scroll-padding-inline-end property.
In this example, snap position is set to end in the inline direction, so the element in focus should snap into place with a 20px distance to the right of the container. But instead, because of the writing-mode value, the element in focus is offset by a 20px distance between child element and the bottom of the container.