Garmin made a change to their API disabling the method by which ConnectStats was accessing historical activities before the first install of the app.
If you have the app already installed and the history downloaded it should mostly continue to work.
If this is your first install, you currently only will see new activities recorded after the app was installed.
IMPORTANT: make sure if you use Garmin that your source is set to ConnectStats only.
Fixing this require quite a big change in the code, and it will take some time. I am also unfortunately quite busy so people will have to be patient, and I hope I will find the time to do this. It is of course frustrating, because it will take a while to just implement something that will bring it back to its original functionality…
If anyone is a computer/php programmer with a keen interest in helping, please reach out to me. The app is open source, free, no advertisement and its data is kept private to you and not sold or shared anywhere. It would really help me if someone sharing the same hobby was interested in helping me fix it, maintain it and even enhance.
Meanwhile, I hope this does not mean the end of Connectstats, the app has been alive for now 12 years or so, it would sadden me to have to turn it off.