This sounds very similar to the old "SPAM-bassador" exploit that was never fully fixed and this used to let you get several hundred ambassadors to stack at Wanderers Skybase to exploit spying on Airless Wanderers. Two hundred ambassadors would give you around +5000% espionage so it was a great exploit.
Get a message with any diplomatic treaty offer, like free trade or defence treaty, and then in the messages you can click on accept or reject or the problematic "show info" option. You click on show info and the empire page opens on left of screen, you can then click on accept on the empire page and this does not delete the original message so you can repeat the trade acceptance in the empire page to get several hundred ambassadors to exploit spying.
Spam ambassadors was the only way I could find to get one month tech stealing on really high level tech when airless wanderers had it before Airless Wanderers having too high tech to steal was fixed.
The steps to replicate this are pretty easy.
1) Get any treaty offer message and open it.
1b) You can pin the message open to make it less annoying to accept hundreds of treaties on the empire page.
2) Do not click on accept or reject.
3) Do click on show info.
4) Empire page opens up.
5) Accept treaty on empire page. Do not accept treaty in message page.
6) Repeat until you hit the soft cap on ambassadors for the version you are playing.
The ambassador soft cap used to be around two per planet when you had a lot of planets with a 50%+ success chance to spawn a new ambassador when you had over 100 planets of any size in your empire, these planets needed an administration facility to add +10% 'appearance chance ambassadors', no idea if this exploit was fixed.
This meant every treaty accepted gave you a high chance of another ambassador and you could get ambassadors in the low thousands in bigger games (as an aside you need some way to mass dump characters with negative traits like demoralizing without having to manually check every leader every few months in game).
The spy spam was a bit more complex but would get you at least fifty spies. Could never work out the formula and soft cap for this. Most spies I ever had was in the low 1000's with a different kind of exploit. This was fixed a while ago but I dont think it was an actual bug fix...just lucky as you fixed something else this exploit relied on.
