This is an old tread but this continues being an issue.
Today’s example:
Route ascent/descent when planned in Suunto app: 9200+ ft.
The same route ascent/descent when planned in Strava : 7426 ft
Actual ascent/descent measured by Race: 7477 ft.
The same route ascent/descent measured by Garmin Epix and Fenix 7: 7800 ft.
This is way off! Most of the time Suunto App underestimates elevation by 10-20%, but I find that in large mountains it seems to overestimate, especially, I suspect, when traversal of steep slopes is involved. At the same time, Strava is pretty much spot on. Too bad, when a route is synced from Strava to Suunto app, the revelation data is overridden by Suunto app.