Fix: Syncing Shared Google Calendars on iOS
If you’re having trouble getting a Google Shared calendar to show up on your iOS device (or possibly Mac) go to https://calendar.google.com/calendar/syncselect and check the calednar(s) you would like to sync.
I do not know why this is not linked on the Google Calendar settings page and it is quite frustrating but this fix should do it.
Of course, I was reminded of this solution today when I was searching for a fix and came across this post on my old Techademic site: http://www.techademic.co/blog/2016/6/fix-syncing-of-shared-google-calendars