UserAgent: Mozilla/5.0 (X11; CrOS x86_64 10895.56.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.95 Safari/537.36
Platform: 10895.56.0 (Official Build) stable-channel eve

Steps to reproduce the problem:
1. Connect your Pixelbook to a 5ghz WiFi network (I tested it with the router "[VideobridgeDual] HGW-500BNA-QCv2", commonly called Arris Videobridge and sold by the ISP Movistar in Spain).
2. Connect your cast-enabled device (such as Google Home or Chromecast) to the same network.
3. Open https://labs.avm99963.com/chrome/sound.php, play the audio, and try to cast this tab to the cast-enabled device.

What is the expected behavior?
The tab should be cast correctly to the cast-enabled device.

What went wrong?
Slightly different things happen if you use a Google Home Mini or a Chromecast (the cast-enabled devices with which I have tested), but in general the content is not casted correctly.

What went wrong with the Google Home Mini: when casting audio from a tab, it plays the audio for less than a second (although sometimes you don't even hear any sound at all). After some seconds, most of the times the Pixelbook disconnects automatically from the 5ghz network (although the tab has the cast icon which shows that it is still casting) and some seconds later it automatically connects again to the 5ghz network. Afterwards, the cast icon in the tab disappears and the Home plays a sound as if something went wrong (the following notes: E E C# C#).

What went wrong with the 2nd generation Chromecast: the exact same thing as with the Google Home Mini, except the Chromecast shows the screen for less than a second and then freezes (or doesn't even show any image/sound and just displays a black screen), and afterwards instead of playing an error sound, it shows an error message which reads: "Cast connection stopped \\ {{device_name}} seems to have lost its connection with your device \\ Try casting again"

Did this work before? N/A 

Chrome version: 69.0.3497.95  Channel: stable
OS Version: 10895.56.0
Flash Version: 31.0.0.108 /opt/google/chrome/pepper/libpepflashplayer.so

I did several tests of this problem with my Home Mini, which I expose here: https://docs.google.com/document/d/1NW59VpRiUmt9770Ork3zoOX9dG7-uBto43HCvhNl66g/edit?usp=sharing

The results are that, although I performed the tests with several WiFi networks, the problem only happened when I connected both my Pixelbook and my Home Mini to my 5ghz network (I couldn't try this with other 5ghz networks because I only have one router which can emit a 5ghz signal). Still, this problem didn't happen with an iMac and the Home Mini both connected to the 5ghz network (or connected to any of the networks), so that's why I guess the problem has something to do with the Pixelbook.

Finally, I found that this issue is similar to  issue 496740 , although I can only reproduce this when trying to cast a tab, not when casting, for example, a YouTube video (which opens the YouTube app in the Chromecast instead of casting the whole tab), as that issue suggests.