Why can't I turn on syncing for some attributes?
You must have data for an attribute in Apple Health already for Exist to start syncing that attribute. Make sure you've synced some data into Apple Health sometime in the past 60 days.
You can check your data in the Health app by choosing the attribute from the Browse tab and tapping "Show All Data" near the bottom of the screen. If you previously did not allow Exist access to an attribute, we are not able to request access to that data again. Visit the Apple Health app to turn on permission for Exist to access this data in the "Data Sources and Access" section for that attribute.