iOS 11 is automatically offloading apps I use

I have an iPhone 6S with iOS 11.1.2.

I have the autoffload turned on, which is great.

Except it off loads my Google Calender App which I use every day.

Looking in iPhone storage, I have found that the Last Used Date for the Google Calender App is May 2017. Even though I use that App everyday (even now I download it again each morning ).

I have tried to manually delete the app completely and reinstall but the Last Used Date still is set in May 2017.

Any ideas?

Thanks