Ethan's Quilava's "Guided by the Journey" ability sometimes can't be activated

Ethan's Quilava has the ability "Guided by the Journey" which is supposed to search out an "Ethan's Adventure" card. However, sometimes this ability is grayed out and cannot be used for no apparent reason; it cannot be lack of Ethan's Adventure cards in the deck, as this has happened even when I have some left.

I haven't been able to find anything in particular that causes this to happen. Sometimes if you take some kind of action, like playing a shuffle effect or a Supporter card, it will be available again, but not always; sometimes you just have to wait until the next turn.