1) The log download feature is still a very new feature and for iOS it’s only available in the beta version of the app (for Android it’s in the production version). To join the iOS beta program send an email with “join iOS beta” in the subject line to “email@example.com”.
2) The internal temperature sensor should not be 10C off. If you’d like to exchange the unit email me (firstname.lastname@example.org) and I can arrange it.
Hope this helps, best