Ethical, factorio, pick one. May I remind you of your war crimes on Nauvis?
All jokes aside, this is an interesting idea. Perhaps you could use the recursive blueprint mod to change the drop off location to avoid overcrowding? Not sure about how to do that in vanilla though.
I've seen this happen on quite a few new releases. I think there is some eventual consistency stuff happening behind the scenes with the steam servers kind of like the old 301 views on YouTube, but for the achievements on steam.