[UPDATE] This is now fixed with version 3.0.2
Since Yesterday a change in the Garmin API resulted in ConnectStats reporting some activities were deleted from Garmin Connect when trying to download the details.
This happens because the part of the API that ConnectStats use to get the weather is now reporting the same error as when an activity is deleted and that confuses ConnectStats.
I will push a bug fix to the store that will stop downloading the weather for now until I can figure a new API to retrieve it.
Version 3.0.2 was pushed to Apple for approval today, unfortunately pushing a bug fix requires a few days, sometimes up to a week for Apple to approve it. Sorry for the inconvenience caused and thanks for your patience