UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/537.36
Platform: Google_Veyron_minnie.6588.237.0

Example URL:
Any

Steps to reproduce the problem:
0. Log out of ChromeOS
1. Log in as the guest user and ensure wifi is connected correctly.
2. Try to cast a tab

What is the expected behavior?
My chromecast shows up in the list.  (It does work on other chrome instances on the same wifi network.)

What went wrong?
Cast popup says no chromecast devices were fine.

However, if I log out and then log in as a real user on the same device (on the same wifi network), it works fine.

Did this work before? N/A 

Is it a problem with Flash or HTML5? HTML5

Does this work in other browsers? Yes

Chrome version: 58.0.3029.140  Channel: stable
OS Version: 58.0.3029.140
Flash Version: 

Contents of chrome://gpu: 

Even if there's a good reason this shouldn't work (I can't think of any), it should give a clear message saying why, rather than just confusingly offering the popup and saying it "can't find" a chromecast.