Found this hack on the web, but it was a little sketch on details, so I though I would refine it a bit.
1. Download “User Agent Switcher” from the Chrome Webstore: https://chrome.google.com/webstore/detail/user-agent-switcher/lkmofgnohbedopheiphabfhfjgkhfcgf
The purpose of this extension is to allow your browser to masquerade as a different device.
2. Said i’m an Iphone 4
I don’t think you *have* to pick iPhone. It can probably almost any mobile agent. But iPhone works.
3. Go to http://m.google.com/sync
This is where you are setting up sync settings for the fake device you are pretending to be. It should look something like below. If it doesn’t, you didn’t change your user agent.
5. Click your Windows mail device
This should way WindowsMail on it somewhere. I have a second one on mine from an old installation of Windows8
6. In the URL is a part which is called “supportMultipleCalendars=false” change it to true
Look at the URL in the location area and find that string. Change the word false to true. Don’t change anything else.
7. Reload the Page.
You can hit F5 to do this, or just hit <Enter> after you change that word.
9. Save. The Save button is way down in the lower right.
10. Re-add your Google Account to your Windows Calendar app. Settings, Accounts, Delete your Google account from with the Calendar app (you won’t lost anything). Then add it back. You should have access to all of your calendars now.
I have no idea why this works, or what is really going on, but it seems to work like a charm.