All, but primarily effects Demi-Deities

Etherealization is caused when a Demi-Deity loses their physical form and their Soul becomes deconstituted. This can occur when Demi-Deities fight one another, gods of higher divinity bring judgement down upon them, or they are attempting to ascend further and fail in that process.

Etherealization can only be cured by the Etherealized Demi-Deity being summoned by another entity, as part of that summoning process is constituting a new body for the Soul to inhabit, and when the Soul is within a body it will be able to reconstitute itself rapidly, having a form to re-adhere to.