Thanks!
Yeah the storm is best guess as well. Maybe the Wraiths and Serpents are in their own class of "specials" and can be spawned in storm during day... It is just that you don't normally get any weather effects in the swamp so that storm spawn of a wraith would be super rare. If intended at all!

Very curious.

Side note - I also avoid the swamp at night unless I am actively hunting for chain. In all but one of my worlds I never even needed that, just getting enough from crypt boxes RNG.