Missing enrichment item for gorillas?

Is there an enrichment item for the gorillas missing in the game? I have researched them fully but in the zoopedia it shows me one enrichment item is still unknown and locked.
How can this be? Is this a bug or how do I unlock that item now?

Same issue here - I managed to unlock the last lion enrichment feeder by researching tigers, but seems odd if that's intended. Still have the rest missing.

It's annoying because it's potluck guessing which animal you need to research to unlock the missing items - I assume it's a bug.

I have all Enrichment-Items for Gorillas unlocked. Bornean Orangutans where the only other Apes in my Zoo until yesterday so I would recommend researching them. I think that's how you would get the Item
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