So I talk to Jiro Sugihara and accept a quest but it just instantly resolves it and disappears from my journal. He still shows up under available the entire time though.

Working as intended. It's just to load up your set of diplomacy missions(or lack thereof if you're on cooldown) under "Diplomatic Investigations" on the next screen.

That's just it, I am on NO cooldown. he GIVES me an explore mission but it just auto resolves and leaves my journal INSTANTLY. Clearly bugged.

All the same here. it's bugging me that i'm missing out on potential rewards and points and such. I was unaware that he actually did missions because i thought it was still a work in progress. But apparently from most people, they tell me it's not.