The current minimum version of ConnectStats is 3.1 to use with Garmin Data. Older version will not work with the latest Garmin API.
ConnectStats also requires iOS 9. It is not possible for me to maintain compatibility with older iOS because I do not have the resources and the time to test incompatibility with older iOS version. I am sorry for any inconvenience. On the flip side, I try to keep ConnectStats updated with latest features of iOS.
Here are some of the history of changes from Garmin that required updates to the app: