Why doesn't FireAllClients work when trying to send?

Code: server:

script.Parent.Triggered:Connect(function(player)
	game.ReplicatedStorage.Open:FireAllClients()
	print("A")
end)

Client:

game.ReplicatedStorage.Open.OnClientEvent:Connect(function()
	print("B")
	openDoor()
end)

Output: A (no B)

FireAllClients Command

When it comes to using the :FireAllClients() feature... I would only use that when you're trying to call to a LocalScript inside of StarterGui/StarterPlayerScripts/StarterCharacterScripts. That's my recommendation but use it as you believe fits. Here's a link that will lead you to how the FireAllClients command works.

Your Error

The error in your script is the script.Parent.Triggered:Connect, after reviewing the script; I realized I missed this MASSIVE mistake. What you need to do is changed Triggered to Touched.

Server Script

script.Parent.Touched:Connect(function(player)
    game.ReplicatedStorage.Open:FireAllClients()
    print("A")
end)

Local Script

Do note that this command may not work if the LocalScript is in workspace, ReplicatedStorage, ReplicatedScriptService, ServerScriptService and ServerStorage.

game.ReplicatedStorage.Open.OnClientEvent:Connect(function()
    print("B")
    openDoor()
end)

As explained in my comment above...

Server Script

script.Parent.Touched:Connect(function(player) --not Triggered
    game.ReplicatedStorage.Open:FireAllClients()
    print("A")
end)

Local Script

game.ReplicatedStorage.Open.OnClientEvent:Connect(function()
    print("B")
    openDoor() --im assuming you have this function defined somewhere
end)