My calendars are no longer syncing on iCloud between iOS and OS

My calendars are no longer syncing between my iPad air 2, iPhone 7 and iMac running OS Sierra. i set up a new apple ID as a test account and all calendar events synced perfectly. When I signed out of the new apple id and back to my original account, the syncing continued to not work. Photos, messaging and email all sync perfectly. Only calendars are not syncing. When I open my calendar apps on my phone and iPad, there is a small exclamation point to the left of the word Calendars at the bottom of the screen