Hi David,
Not sure if this is a bug or a Garmin issue. I swam few days ago and I did a 400 / 200 mt test. (Just before the test, during warm up my Garmin FR935 froze and I had to restart it and I wonder if this might have an influence). I did two PB for both distances (at least season best).
As you can see in the screenshots the two intervals were detected but only 200m is recognized as a PB. In the Pace page for 400 mt you can still see my previous PB.
I do not understand why the interval 400mt @1:41 was not recognized as a PB.
Thanks