I have verified that, in all the activities uploaded from Suunto and Race S watch, the elevation gain is higher than the elevation gain recorded both in wath and Apps (and also in other platforms). This behaviour happens only with activities recorded with Suunto Race S watch, no problem with Vertical in same activities.
Do you have that behavior?
Go to The activity… Action → Settings → then Use Elevation Correction (turned OFF). This is when your Watch has a Baro and this will force intervals.icu to use the baro data instead of getting the data from maps topo