Likely a modern elaboration of Mel- names, associated with sweetness or melody by sound.
Meldia is likely a modern elaboration of Mel- names, associated more with sweetness or melody by sound than with a single old source. That makes it feel intentionally musical and lightly decorative. The spelling is compact, but the sound remains gentle and flowing. Meldia has a modern softness, the kind of name that seems designed to feel pleasant, graceful, and easy to say.