Because it is broken. The workaround is to change the activity type to one of the top-level types such as Running or Cycling. If you use the child activity types like Street Running or Mountain Biking the graph will appear without data.
Because it is broken. The workaround is to change the activity type to one of the top-level types such as Running or Cycling. If you use the child activity types like Street Running or Mountain Biking the graph will appear without data.
It is not clear that Garmin is aware of the problem or not. There about 50 posts on the topic here, but I'm not sure anyone has actually reported it. If you wish to do so, you could do it here.
The run cadence chart for my run earlier today, recorded using my FR635 and a connected HRM-Run chest strap (which provided Running Dynamics data, including cadence), appears just fine in Garmin Connect online. My fiancée, who was running with me and recorded her run with a FR235, could see her run cadence chart in Garmin Connect Mobile (but she doesn't use Garmin Connect online at all, so I'm not going to ask her to check there).
Just checked GC online, and the cadence shows up there, but still not in the mobile app (same activity). Ind addition, I sometimes get a chart with single-leg cadence in mobile - not sure when this happens though.