Open-water swim distance differs from the track recorded? (Todays swimrun 352m vs. approx 750m, unacceptable)

What is your strokes/min? 

Also what is your strokes/min? I'm thinking could that be the thing that somehow could explain it still. As I'm seeing bad with 18 strokes/min, but pretty good at 21 strokes/min. At least no much other ideas currently.

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Would be interesting if you are up to the challenge trying to half your strokes/min for one 550m lap and record that as own activity, is it still accurate for you :) 

Ok, so then that explanation does not work, and no need for KevinJames to try half cadence...

So then, no idea. MarcinKoprowski and you were using the OpenWater activity? Not part of some multisport?

As I've seeing big problems in the distance when part of multisport (swimrun), but the OpenWater is pretty close, still too short, but more acceptable error there.

Yes, im using open water, but will try mutisport tomorrow to xheck if there is any difference. Firmware of my watch is 10.10.

one observation i had was when i was swimming in the wetsuit - the difference was still there, but smaller (1200m measured vs 135 0m real). The stroke rate was the same, 30/mins. Dont know if that was just coincidence, as my stroke is not sifferent in the wetsuit (my legs are bit higher, though).

Yeah I see biggest errors with swimrun and I'm using hand paddles there. But it would feel just so stupid if Garmin would have some distance calculation based on strokes as that's so wildly dependent on the persons technic, having wetsuit, waves, hand paddles, you name it. So I kind of don't want to believe that.

But if with wetsuit you got closed to the "stroke length" then the difference got smaller.
And if I'm seeing bad results with swimrun, being totally too short for using hand paddles, which makes me go further per stroke.

These could fit to Garmin having some stupid strokes*distance algorithm.

Maybe one thing to look is then is there some correlation on strokes and distance.

Couple of OW swims:
2394 strokes, Garmin distance 4248 m, distance per stroke: 1.7744m, real 4360m, 1.8212m per stroke
2722 strokes. Garmin distance 4754 m, distance per stroke: 1.7465m, real 4813m, 1.7682m per stroke.

Couple of swimrun OW swims:
240 strokes, Garmin distance 280 m, distance per stroke: 1.1667m, real 507m, 2.1125m per stroke
341 strokes, Garmin tistance 400 m, distance per stroke: 1.1730m, real 745m, 2.1848m per stroke

Interesting.. distance per stroke are pretty similar in those and the OW ones are pretty ok accurate, somewhat shorter than the GPX track, but the swimrun OW's are like about half the real distance.. and I would guess that with hand paddles I would go further with stroke even I have shoes on me etc. So looked also the GPX distances and length per stroke there.

Not seeing any insightful results from this and doesn't seem like there is strokes*distance at play.

Frankly, i dont see us as those who should figure out where the problem is, as we cannot fix it anyway.

I hope once we report some repeatable “bugs” Garmin will look itnto it to solve the problem.

What I've understood this issue is not totally new and has been there for long time and it is not just for 955.

But at least in my 945 swims I haven't seen anything like this in recent firmware versions (at first it was total dumpster fire also, loosing OW swims totally).

And even we can't fix the issue, if we understand what would be causing it depending on the reason causing it, one might be able to do some workarounds, or point that you are getting bad data because of XYZ. And at least for me it's interesting to try to understand the issue and it's root cause.