I've upgraded to WatchOS 2 (13S5254w) and I'm unable to see my Gmail calendar events on my watch. I can still see my iCloud calendar events, but not any third-party calendar.
On my iPhone 5 (iOS 9 beta), I can see all the events from my different calendars just fine.
I have already added the UUID of both my iPhone and Watch to the developer devices list. And I have tried restarting both devices. I have also tried removing/adding the calendar glance, and customizing the calendar glance. But nothing seems solve my issue.
Nevermind, virtubob's answer in this thread helped me: