Final Championship Chest not opening [Gameplay]

I had bought 2800 RP upon seeing the Championship chests and bought the 11 pack. I had opened 10, but upon having one chest available, I am unable to open it. Screenshot is provided.

Step 1: Buy 2800 RP Step 2: Buy 11 Championship Chests Step 3: Open Championship Chests Results may vary.

Edit: Forging a hextech key resulted in it being able to open, which is weird considering it was part of a bundle.