Elevation change calculation: locusmap-brouter vs mapout

I use LocusMap Classic (full licence) with Brouter and my partner uses mapout for Apple. I also have a non paid version for LocusMaps 4.

We calculated a route from Dongpu Lodge to Yushan peak in Taiwan and found a substantial difference in elevation gain between the two apps: LocusMaps calculates 2300 m up and 1000 m down; Mapout Calculates 1700 m up and 400 down.

(Figures rounded)

That's a substantial difference, more than the 10% estimated by other online blogs.

Which would be more accurate? How could such large differences in calculation come to be?