If JOIN is unable to read your Strava activities and use them in calculations, it may be because you have not granted permission for JOIN to access private activities in Strava. To fix this, try reconnecting to Strava and make sure both checkmarks are enabled. Alternatively, you can change your Strava settings from 'private' to 'public'.
It is also possible that you have the wrong Strava account linked to JOIN. If this is the case, you can follow the instructions at this link to fix the issue: https://help.join.cc/hc/en-150/articles/5440468599441-Logged-in-with-the-wrong-Strava-account-