Garmin Connect and Strava dealing with an obvious anomaly

Did a nice ride today aimed at two of the 100 hills in Kent/Surrey. Flew down Titsey Hill – it was early and quiet – but really surprised when my Garmin Forerunner gave my vmax as 109 mph! Put it down to maybe hitting a bump or a swerve causing a spike in the data or machine.
Uploaded data to both Strava and GC. GC still shows vmax as 109 but not surprised as it is a Garmin device. Strava shows vmax as 84 kph which makes more sense – most of my fast downhills have been around 53 mph and doubt me and my bike can get much more than that – not that I want to! When I check the segment for that hill the average speed is 86 kph but max is 84. How does that work?!