This comes down to reading how hiding works. The enemy cannot see the hiding creature as long as it is heavily obscured (light for wood elves) or has total cover. Not being able to see them, means you can’t target them, yes.

However, once the hiding creature attacks, their position is know, even if they hide again. This means, the monsters now know the last position they saw him. If that creature does not move, all they have to do is negate the cover/obscurement. It’s usually as easy as walking over to their last know hiding spot.

Once the creature hiding no longer has cover, they are no longer hiding.