Problem: Unable to snap to new sketch's vertices when creating a new line or a polygon
When first creating a new line or a polygon, the ability to snap to the new sketch's vertices is not available when snapping has been set.
This is intended functionality because the sketch is not actually a feature until the sketch is finished.
Solution or Workaround
To snap to vertices or an edge in the sketch, check the option in the snapping menu to edit the sketch.