GoogleCalendar is not displayed on iPhone6

The Google Calendar shows on the iPhone 4s, but not on the iPhone 6. Why?

I put Google Calendar in the new app. Because of battery trouble with my iPhone 6 I used my iPhone 4s. Today I changed back to iPhone 6 and downladed the test verison of my app. The G. Calendar does not show. I checked the web version and everything is ok. Why does the calendar not show on the iPhone 6?

Best regards,

Gro