Hi ​@Johutch, that looks like one of your activities got corrupted and messes the stats. Scroll through your activities from the time it started happening to find the culprit. You can either try to crop the problematic activity or delete it, that should fix the problem (including the graph - the messy activity had made the actual weekly mileage so insignificant that it's almost invisible on the graph due to the huge peak). If that activity is somewhat important for you, you might want to export it first before deleting it from Strava, edit / correct it with some 3rd party tool, and import it back once corrected. 

If you can't find the problematic activity, post your Strava profile link here and we can have a look (but you’d need to have a public profile - we're users like yourself, we can't see private activities)