Today
In Course of Terror, after completing all 4 Rounds and obtaining 10 Treasure Keys, I am unable to open any of the chests with these keys. I still receive 50 Phirius Shells from the minigame.
On the last round (Round 4), I was able to obtain 1 Precious Key and used it to open one of the special chests. I was not able to open any other chests. I opened the Special Chest first, then tried to open the others, which I was unable to do.
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Yesterday
I was able to open all 10 chests using 10 Treasure Keys, and 1 Special Chest using a Precious Key. However, I had 2 Precious Keys and was not able to open the second Special Chest. In this case, I also was able to receive 50 Phirius Shells.
Thank you. I will keep you updated with my actions in future Course of Terror minigames.