Had same reboots (usually after 2000-2500m) on 7.51 ((. Have not used HRMSwim.
I think it is often happening when i use Garmin player (playing my tracks, not Deezer or Spotify) before swimming.
Now i just power off/on my Fenix before swim and it works !
I use HRM Swim. Never had an issue to 7.1
It happened to me 4 times last 30 days. Software version 20. It's quite annoying as 2 times I have lost the whole activity.
SW version 20? That's a Fenix 5 - not 5Plus so might be different. Don't see recent post on the Fenix 5 forum about this. You probably did all the obvious like rebooting and checking the filesystem on the watch is not nearly full?
Yes It's a Fenix5 and I have tried all advises but It still keep rebooting. While swimming and running, Probably I should have post it on the other section related to Fenix5.
In case you didn't try it yet.. uninstalling any non-stock watchfaces and data fields might help. To determine which one was the culprit, re-enable them one by one.
On the Fenix 3, activity-apps could get sortof corrupted and you'd have to reinstall them. I'm not even sure if that is possible on a Fenix 5 with core apps like running and swimming.
Can you think of anything the reboots have in common? Alerts, events?
Just for fun remembering: causes of reboots on some older devices: some Fenix 2's, when the battery was over half empty and a vibrate alert went off, it caused a temporary power dip that caused the watch to restart. The original Fenix could get "overworked" when pressing buttons during an activity with GPS, would freeze and restart.
Thanks for your reply. I have uninstalled any non-stock watch faces and data filed but still occurring. Today I was swimming and suddenly I have received a weather alert on the phone and after few lines I have noticed that the activity was stopped without recording anything.
I forget if you did a "reset to factory defaults" yet, if you already have, I'm afraid there is nothing much except calling Garmin Support. Or maybe try with the phone connection off, and no sensors connected, right after a "factory defaults"-reset. If it still reboots in that condition, it's quite certainly faulty.