This is a very specific question, so maybe I can't provide you with enough information to help me solve the problem.

It's an issue of triggers and events.

I have triggers that have a condition and events to fire off.
I have a Trigger Handler that sends events to active triggers.
The triggers check the event against their condition and if the condition is met, it fires off its events.

My world consists of a bunch of rooms. Each room can have triggers in it that are moved into the TriggerHandler when the player enters.

I have trap rooms that have an area trigger that closes all exits. These rooms also have kill count triggers that opens the doors when all enemies are killed.

It all works splendidly.

The problem reveals itself when the player dies or saves the game in a closed trap room. Now the doors are closed when the player returns, and so they can't enter.
I figure I could maybe solve the death issue by having a PlayerDiedTrigger that opens all doors in the room and resets the triggers.

Saving feels more difficult. There are other doors that need their states saved, so I have to save whether they are closed or not. Not only that, but I have to save the state of the triggers too (I don't want the player to have to redo the trap rooms they've cleared), so even if I manage to reset the doors with some ugly myShouldResetWhenLoaded flag, the trigger that closes the doors has already been triggered.

I can probably figure something out, but it feels as if any solution I come up with is ugly as hell. I don't expect anyone to know an exact solution, but maybe someone could point me in the right direction?

Ah, maybe the missing piece of information is that upon loading a saved game or dying, the player is returned to the entrance of the dungeon.

So if the player saves the game in a room where the exits have been sealed, there's no longer any way in there and the dungeon is unsolvable. And if I write code to force the doors to open somehow, the area trigger that seals the exits is no longer active, so the player would have bypassed the trap room without having to fight.

I'm starting to consider just putting a isTrapRoom-flag in the room and solve it that way, but I have a feeling that'll lead me on a path where rooms have a bazillion update and activation functions depending on their combination of isTrapRoom, isShop, isInside, isUpsideDown, isDirty, isDangerousToGoats and smellsOfElderberries flags...

What I would do is simply not save the states of doors or door lock triggers at all. This way, when the player re-enters the dungeon, either via death or save/load, the dungeon returns to its original state with regard to trap doors. Monsters and items can still be saved off, though, so it's possible for the player to partially complete a dungeon and then revisit it entirely, but not abuse the system by just respawning a lot and gobbling up dupe items/monster XP.

That would probably work for the trap rooms specifically, but there are also doors which are opened by keys that the player picks up. The dungeons can grow quite large, and forcing the players to find the keys for all the doors every time they die seems rather... brutal. So the state of some doors must be saved.

There's always the option of special-casing the doors, I guess, and not saving the state of the trap doors, but then I instead run the risk of having a billion different door types in the end, instead of a billion different room types.

It feels like there must be a more general way of doing this without changing the game design around.

Thinking of it by a moment.... if you are using a database, you could have 2-3 columns:

enteredDoorLock
passedDoorLock

This way you can check if the player already entered in the locked room, and if he passed it. Thus restoring the dungeon "should be a brezze"

If I understand correctly (I'm not using a database and have no experience with doing so), that means I must tag the room as locked instead of relying on a more general system of triggers and events. I'm leaning towards your solution, but I'm not very happy with it, as it'll mean that if I want to create other types of rooms later, that means a bunch of special cases for each one, instead of just adding other triggers.
Then again, I could luck out and realize that the trap rooms are the only special cases, in which case I'm wasting my time thinking about this too much.