Melinoe's parentage is really interesting. It's important to note that the Orphics believed that Zeus and Hades/Plouton were the same god.
This is because Zeus was portrayed as having an incarnation in the underworld identifying him as being Hades and leading to Zeus and Hades essentially being two representations and different facets of the same god and extended divine power.
The Orphic Hymn to Melinoe also references this by mentioning that Persephone was impregnated upon the bed of Zeus Kronion in the Underworld by the River Cocytus.
The idea of defining Zeus as Hades has been present in Ancient Greek literature from Homer to Nonnos.
Hence the Orphics stating Zeus Kronion impregnating Persephone in the guise of Plouton, was just a reference to Hades having a role that links him to being both Zeus and Plouton in the Orphic Mysteries.
The different cultures of the Hellenes had different traditions that were then looped in under the worship of the Theoi. Some stories were later changed for continuity and many different things were said about many different characters. In Hesiod’s Theogony, for example, there are two different parents for the Muses– in the same poem no less!
Aside from the Orphics, it is believed that Melinoe being called the daughter of Zeus is due to her being syncretised. You can read more about it here: therkalexander.com/post/715041…
Growing up, my Hellenic grandmother told me that Makaria, Melinoe, and Zagreus were Hades and Persephone's children; despite the fact that ancient sources claimed otherwise. Though there are ancient sources confirming that Hades and Persephone had children without naming them.