I mean, it’s not called Locate Traps
Actually, Find Traps is interesting due to its name. Does that suggest something about how the designers use the word "find"?
We might generally think about three different ways of naming the trapfinding spell:
- Detect Traps
- Find Traps
- Locate Traps
"Detect" is used on spells like Detect Magic, Detect Thoughts, Detect Poison, etc. That's where you examine an object and determine whether it has some property — if it has magic, what its thoughts are, if it's poisonous, etc.
"Locate" is used on spells like Locate Object, Locate Creature, etc. This tells you the direction in which something lies. It narrows down your search space, but doesn't give you a precise location until you start triangulating.
"Find" is used in two separate spell lines, Conjuration (Find Familiar, Find Steed, etc) and Divination (Find Traps, Find the Path). Since Divination is more relevant to our concerns here, "Find" seems to equate to "gain awareness of".
So with that in mind, you would expect a Detect Traps spell to be able to tell you if a specific thing you're examining is trapped; Locate Traps to give you a direction towards a (specific?) trap; and Find Traps makes you aware of traps around you. The fact that it doesn't tell you exactly where the traps are gives us an understanding of what "find" entails, as well as some leeway on how it applies to hiding.
We can then extend this understanding of their use of the word to how it applies to the Hide action, and how its Invisibility is overcome. Namely, that an enemy gaining awareness of you counts as "finding" you. There are lots of ways that could happen, the simplest of which would be seeing you.
But other things might happen. For example, a guard is patrolling a warehouse. Your rogue is trying to stay out of sight, having hidden, but accidentally bumps a shelf and knocks over a box of tools (we'll ignore the more specific bit about making noise, which is just a subset of being found). The guard is now aware of you; he has "found" you, even if he hasn't seen you. At this point, you lose the advantages granted by being Invisible; you no longer get advantage if you attack the guard, nor does the guard have disadvantage attacking you (though he can't attack you if you're behind total cover, and he can't see you).
Now, if you're still out of sight, you can attempt to Hide again so that he loses track of your position. Maybe you imitate a cat's meow to make the guard think it was just some animal causing a ruckus, in which case you revert to being Invisible. But if he rounds the corner of one of the aisles and sees you, your cover is blown and you'll probably need to run.
Overall, if we go by how Find Traps is named, "finding" you appears to be becoming definitely aware of your existence, with enough information for someone to put their hands on you with a little effort. It does not require being able to absolutely pinpoint you or identify you in that moment, but it does mean you don't get the advantages of the Invisible condition. You're no longer "outside" their conscious awareness.
Being in line of sight isn't necessary for being found, but being in line of sight also doesn't guarantee that you're found. You might be in line of sight while mingling with a crowd, but if someone can't readily distinguish you from anyone else in the crowd, he hasn't found you. If you walk up to a guard all by yourself, you will certainly be part of his awareness, and thus be "found", but if you're part of a mob at the foot of the hangman's platform there may not be an awareness of you in particular, in which case you might still be considered Invisible, and be able to launch a surprise rescue at a critical moment.
You also only lose the Invisible condition if an "enemy" finds you. You could be Invisible in the middle of a crowd. The crowd aren't "enemies", so whether they can see you or not doesn't matter. Whether your buddy can see you likewise doesn't matter. The shopkeeper that you just robbed who's chasing you, however,
is an "enemy", and it's whether or not he finds you that matters.
In fact, the "enemy" portion also comes up earlier, in that you have to be outside of any
enemy's line of sight, not outside of
anyone's line of sight, in order to Hide. So you can hide in a crowd, as long as you have a moment unseen by any 'enemy'.
And then "enemy" carries the system even further. You may disguise yourself as a beggar to get through the city gate. The guard at the gate is an "enemy", and you are "hidden" from him, effectively Invisible, unless he decides to start checking for identity cards. If you don't have one, then the guard "finds" you, removing the advantages you might have had if a fight breaks out. However if you made it through, but your buddy didn't, and a fight breaks out, you're still technically Invisible, and get advantage on the initiative roll, as well as the first attack you make because the guard wasn't expecting an attack to come from you.
Summary:
The "Find" bit actually does a fair bit of heavy lifting in this system. It's deliberately vague because there are so many contexts it can be used in that no specific list could cover them all. In fact, the other three conditions that break hiding's Invisibility can all be considered subsets of the simple "find" condition, but broken out because they are extremely common, and there shouldn't be any question about them (though even then, there are circumstances where I might tweak what counts as "too loud", for example).
Likewise "enemy" is extremely relevant in how this interacts with both gaining the Invisible condition and losing it.
The Invisible condition grants you certain benefits. Using Hide grants you those benefits by removing your presence from the awareness of particular individuals. The Invisibility spell grants you those benefits by making it impossible to actually see you.
The Invisibility spell grants you those benefits even if you're clanking around in full plate armor. The Hide action grants you those benefits as long as you're careful of your behavior, and you don't place yourself in a position to get specifically noticed.