Course ascent differences between Connect, Strava, Komoot, Garmin overstates wildly.

Hi :-)

Does anyone know why plotting courses on Connect/Garmin results in such different ascent information compared to Komoot/Outdoor Active etc?  Connect/Garmin seems to wildly overstate the elevation compared to the other platforms.

A 160km route in Yorkshire, plotted in Garmin gives total ascent of 3517m.  The same route on Komoot/Strava/Outdoor Active is 2700m!!

Many thanks for help

David