I cast Invasion of Ikoria, 2g +X, X = 6, tried to put Ulvenwald Hydra in to play 2G 4 colorless, last time I checked 2 + 4 is 6, so it should have let me put it into play. It didn't.
Pretty Sure Invasion of Ikoria Reads, search your library for a NON HUMAN Creature with Mana value X or less, and put it into play. If you Search this way, shuffle your library. So I paid 8 mana for Ikoria, and searched, and found a 6 mana Creature, that wasn't Human, but it wouldn't let me put it into play, I even had 5 mana, 4 mana, and 3 Mana creatures in library, it wouldn't let me put any of them in to play. So am I doing something wrong, or is it bugged.