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For the whole situation, Guide Dang It!.
For the hint itself, not quite as sure. Something that you miss on a first playthrough but might notice as more important on subsequent playthroughs would be Foreshadowing or Rewatch Bonus.
Edited by KD
I'm not quite sure about the Foreshadowing and Rewatch Bonus because in the example which caused me to seek a trope for it the hint is so stealth that it can be completely missed on multiple playthroughs even to the point the player achieves the golden ending without actually knowing about the hint.
The example in question is the finale of Fragile - a locust-like monster appears before the little girl protagonist and she has the option to either shoot it with the handgun or hold fire. The monster in question is actually a trauma-induced hallucination of her dad and the only hint the player gets is the monster wearing a moon-shaped hairpin on its neck - the same one the father is seen wearing in the flashbacks. It is so badly visible that you can actually get the good ending simply by a mixture of Violation of Common Sense and resorting to pacifism without even learning about the hint.
Humankind is like a train. No matter how powerful the locomotive is, it can only travel as fast as its slowest car allows it to.
Guide Dang It! is the one you want.
Say you're dealing with an important event within a videogame that has severe consequences. First time you solve it how your instincts or wits or whatever tell you only for it to go horribly wrong or at least not as well as you were hoping for.
Then on the second playthrough or after reloading a save you discover a tiny detail that hints the boss monster isn't what you think it is. You hold your fire and ... turns out it was your mom/dad all along and you were just hallucinating. Yay you get the ultra-happy Golden Ending.
Now is there a trope concerning the hint itself?