I imported 3-4 months of fit files and all the elevation data is off typically a lot higher. I've since learned to disable the automatic elevation correction which typically adds more. I use a 920xt so I think the data I get is pretty good.
Here is an example of where the 920xt fit data was imported inaccurately which seems to be a bug. I'm linking to my garmin activity: https://connect.garmin.com/modern/activity/2732358752
I'll attach the fit file too.
The geonames.org (Aster) correction gets me closes to what appears in Garmin. But still almost 2k feet higher.
If I remove all correction, then I get 6,345 ft which is significantly higher than the 2,959 ft on Garmin. I've ran this course multiple times and it's very popular. The garmin data is close to accurate. But why wouldn't the fit file elevation data be the uncorrected amount in runalyze? Where is the 3k+ ft coming from? A bug?