Garmin Connect open swim wrong distance, correct distance when loading gpx file

Thanks.

But if I open the gpx file with Garmin Connect it shows there correct distance, whereas it does not just after saving the activity.

The watch records the activity as a FIT file, and the FIT file is also used in the Connect Portal. If you export the FIT file as a GPX file on your computer's hard drive and import this GPX file back into the Connect Portal, you will get your correct distance back even in the Connect Portal.

Your problem is not just related to swimming. Garmin includes the accelerometer in the FIT file in addition to the GPS when recording an activity. This algorithm is obviously designed too aggressively. 

The GPX file contains only the position data, but not the smoothing by the accelerometer.

solved

The GPS points are present in both the FIT file and the GPX file. You have no influence on how the smoothing algorithm used affects the FIT file.

In relation to the settings possible by the user, each user has his own values that bring the best result for him. There may be situations in which smart works better than second-by-second. But it can also be different. This is also the case with the satellites used. I live in Europe. There, actually using Galileo should bring an improvement in the track. One would think. For some it does. But not for all. I personally have the best track with GPS alone.

I don't swim (as a sport), but could imagine that second-by-second recording is better than smart for that.

The problem that the FIT file is excessively smoothed by the accelerometer remains.

We have no influence on that. Only the Garmin engineers could change that.

Look here : https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/fenix-6-series/230437/fenix-6s-open-water-swimming-under-reporting-distance-pace

It's an old issue, never addressed, reported thousands of time since years and affected also other devices like 945. Solution, for me, it's to use another watch for swim (Suunto 9 baro), or i always have to correct distance after saving activity. There are also other open threads for this issue. I also made a video for demonstrate it : https://youtu.be/M88WksWOn1w .

Also if you sync activity to strava and than correct distance with Strava, you'll find that distance reported by watch is totally wrong (understimated). Garmin seems don't care about it.

You have to kick them almost once a week > 2 years, like we did with the “doubled elevation plot issue”. I don’t like that ignorance about long time known issues…, no good customer care

I just checked and it was set as smart. Do you think that is the root cause?