So, I started playing D2 yesterday at home. No lag, easy gaming, liked it. This morning I tried the game at the office (100/100/40ms) and the experience was unplayable. I then tried out my mobile usb hotspot with (40/30/20ms) and the game ran very very well.
It seems there are some connection issues with Stadia :0 and it may not be simply about the download/upload speed. Luckily I have (so far have had) a good experience playing at home or with my mobile (a really cheap Nokia 2.2 btw).
Are you using the ChromeCast ultra? I read on a Washington Post Review that it doesn't support WPA2-Enterprise. That could be the cause if you are using a ChromeCast:
Ahead of launch, Stadia warned reviewers that playing on a Chromecast Ultra at work is not supported, as “Chromecast does not support WPA2-Enterprise networks. Stadia’s TV experience with Chromecast is designed for home networks where the Stadia controller and Chromecast are on the same Local Area Network.”
I've also had great a time playing at home, no lag and good experience. But haven't tried it at work...