In Google Calendar I have a shared calendar called "Public Holidays". I can see all events of this calendar in Google Calendar and macOS Calendar app:
On iOS 10, I imported the Google account with all calendars. I can see the "Public Holidays" calendar in iOS calendars list. I don't see any events of the "Public Holidays" calendar in iOS calendar view and neither in the calendar widget.
Best Answer
I deselect shared calendars here https://calendar.google.com/calendar/syncselect and saved the settings. Then I select them and save it again and now it works.