Ascent not correctly calculated

I have noticed, that the displayed ascent is way too low. I climbed from 200m to 400m and the ascent value only increased by about 120m.
Over the whole trip The app said I climbed a total of 418m. I went from about 200 to about 400 twice and had 4 smaller ascents of about 50m each. That should total to 600m. Plus some smaller ascents.
I uploaded the gpx file to and according to their report The total ascent is 681m.