It's not a bug so much as a poorly implemented addition to the log they added a while back. Almost every fish has ???'s for their conditions, whether they are big fish or regular fish. The only fish that they bothered to add details to seem to be the ones used for weekly collectibles and a few random others, most of which are just "none" across the board which is basically just as unhelpful. I, too, wish they'd actually use this feature more fully, but it is what it is intentionally as of right now, and not a bug sadly.

Oh, and the displayed conditions don't change depending on whether you've caught the fish or not. Any fish that has ???'s will always have ???'s even after you catch it.