The only thing that comes to mind is some kind of timing attack. Send loads of requests specific to a company you’re trying to spy on and if it comes back cached you know someone has sent that prompt recently. Expensive attack, though, with a large search space.

I habe come across turning on caching means the llm has a faint memory of what was in the cache, even to unrelated queries. If this is the case its fully unreasonable to share the cache, because of possibility of information leakage.