Unusable Distance/GPS Open Water Swim

Noticed the same.  When swimming my my daughter and her apple watch, and then comparing to google maps using the distance function from point A to point B across a lake, the apple watch 3 and google are spot on.   The 945lte will gain a yard a second a lot of times when just standing still.

How is your GPS recording set?
Settings => System => Data Recording => Frequency

Smart

try switching to 1 second

For sure that will help, however, this wasn't an issue on my 935 when in Smart recording.  And secondly, doing ironman and ironman training, smart drains the battery bad enough.  1 Second will never make it. 

As the OP stated his 920 is fine also, so it is def a prob on the 945lte.

I came from a 935, it was awful for Swim tracking (well.. over the years they changed the algorithms a few times in firmware or GPS firmware and it got better / worse with each change).  It seemed to record points so infrequently that you could only get accurate recordings if you swam long straight lines and were lucky to get a point recorded at a turn or turn around.

My 945 LTE has been really good for GPS swim tracking by comparison.  I can't say the distance is recorded within a precise number of yards, but I have recorded several times with a separate GPS device in my swim buoy and the tracks look really good.  Even short ~50 yard turn around and back for a slower swimmer show up with decent detail (the 935 would have missed completely).

Sorry to not have an answer for you.  It's true I use 1 second recording but I really don't think the setting even applies to OWS since they apply alternative data filtering in that activity type anyway (i.e. if you check your swim file I don't think you'll find 1 second recordings of position even if set that way).

When you say it's wrong and much too short, do you have a reference for what is correct and how different they look and are off in % error?  Like I mentioned, I can't say my 945 LTE is perfect, but it is consistent, the GPS tracks look reasonable and my distance seems ok.  I want to say it's measuring 10% short and I'm faster than it claims, but it would probably be wishful thinking

hmmm.  thanks for the replies people.  always good to share information.  weird how all models are so inconsistent from watch to watch even within their own model line.

I will go to the pool this evening for my 2nd post-covid swim and will do this in open water mode. My fenix 3HR catched the 1.000m distance very close to 993m a few month ago.

I suppose you're free to use any activity type you wish, and if you see good results... that's fantastic.

Personally if I am swimming in a lap pool, indoors or out, I think I would use Lap Swim.

I don't currently have an expectation that OWS will track lap swimming effectively using GPS.  If I had experience with a dual band GPS in a 955 maybe I'd change my mind (still, what would the point be...) but realistically with a watch that's underwater most of the time expecting accurate GPS readings for a 25yd/m or 50yd/m pool feels like asking for trouble.

Good luck with the return post-Covid, I hope all goes well.