Got a response. Didn't have time to test it, but write here if this works.

Google Chrome recently released an update that changes the UI of the casting function, this causes the "blurry" screen issue when trying to choose a casting device or a video. This issue occurs on the Google Apps version of Videostream. We have logged the bug with Google and are waiting to hear back. For now, the issue can be fixed by following these steps:

1. Go to chrome://flags/
2. Search "Views Cast dialog"
3. On the "Views Cast dialog" feature, change it from "Default" to "Disabled"
4. Search "Upcoming UI feaures"
5. On the "Upcoming UI features" feature, change it from "Default" to "Disabled"
6. You should see a prompt on the bottom left to restart chrome

Happens to me as well.
I sent the team an email and will update on a response.