The new Unearthed Arcana gives a new option for warlock’s patron: The Undead. One of its class feature is Spirit Projection:
Your body is now simply a vessel for your spirit. As an action, you can project your spirit from your body. The body you leave behind is unconscious and in a state of suspended animation.
This is just an example of effects that cause spirit or soul leaving their body. There are other similar effects like, although different, astral projection and magic jar spell.
When out of their body, does a soul or spirit count as (normal) creature? Can they be targeted by effects? Can they be seen? What happens when either the body or spirit/soul targetted by an effect? Do both got affected?