The adjective elusive is someone or something that is difficult to find, describe, remember, or achieve.
Synonyms are ambiguous, fleeting, puzzling, or incomprehensible.
The word origins from Latin (1719) elus-, and past participle stem of eludere meaning “elude, frustrate”.
Though that is a common animal, they still find it surprisingly elusive.
It’s unfortunate that the right content is frustratingly elusive.
As much as I don’t want to disappoint you, the answer remains elusive until now.