I investigated this and found a couple of issues. The topo maps don’t seem to do well in your area so you should turn off elevation correction and flag your watch as having accurate elevation. That will be used as the default for future activities with the watch:
When the device is set to have accurate elevation then Intervals.icu will keep the total elevation gain info from the fit file and not recalculate it from the altitude data. Usually this will then match other services. If you crop the file then it is recalculated from altitude data.
You can do Actions → Reprocess file to fix existing activities.
There was a bug that caused climbing to not be recalculated when elevation correction was disabled for an activity. I have fixed this and will deploy later tonight or Tuesday AM.