Zitat:Shan'ze Ritual Stones Drop Limit
Just to clarify on drop chances for ritual stones and keys, you can only obtain one Key to the Palace of Lei Shen (aka treasure room) from any creature on the island, including the Isle of Thunder Rare Elites. Once you’ve already looted one off of a creature, no more will drop from creatures for your character that week. Additional keys can potentially drop from other select sources, but are extremely rare and not something you can try to farm.

Similarly, you can only obtain one Shan'ze Ritual Stone from an Isle of Thunder Rare Elite per week. You'll still be able to collect more from other sources, though.