Duplicate Keys

My initial question for you would be whether you are using the Trial Keys immediately after receiving them or if you are trying to store them to use later.

The reason I ask is that you can only "hold" a single Trial Key at a time; if you haven't used the one that you already have by the time you open your next Red Chest the Key that you already have will be replaced by the next randomly awarded Key.

This is the only circumstance that I'm aware of where you will receive a "duplicate" Key; because the Key of the same color which you were holding previously was dumped as the next Key was randomly selected as your prize; I've never heard of anyone using a Key to open one of the Trial Doors only to receive the same color Key again in the future, but it does happen to people who haven't used the Key that they received in a previous Chest.

I've never heard of this happening to anyone before; have you tried approaching the other doors to the other Trials to see if any of the keyholes light up when you approach closely just on the off chance that maybe the wrong card was displayed?

If you actually did receive a duplicate key then I'd probably suggest contacting customer support to see what they might be able to do for you, if anything.