Your stats in VeloViewer are only as good as the data that is passed in from Strava, and around 1.5% (based on sample data I had a couple of months ago) of Strava segments seem to have bad data associated with them. The 2 main culprits are dodgy elevation data and non-matching distance data.
This isn’t entirely Strava’s fault although I believe there are ways that they could clear up the majority of these things automatically. But for the time being it is up to us, the Strava community, to tidy it up the best we can which will also result in much more accurate stats in VeloViewer.