Every time i try to turn off the gesture setting for backlight for not during activities, it doesn't remember it. Do you guys have this too? I'm on software version 6.0.0
This sounds like the Watch vs Garmin Connect alarms and settings sync issue, as a setting on the watch is being overwritten on sync with Garmin Connect, except the backlight gesture setting is not a device setting available in Garmin Connect. The only suggestion I can think of is to remove your Fenix 5 pairing from Garmin Connect, the iPhone Bluetooth settings and from your registered devices when you log in to my account at the Garmin.com site (when you set up a Garmin Connect account, you also get an account here and any devices registered on Garmin Connect are also registered here, but don't get un-registered when you remove a device from your Garmin Connect account). Once that is done, ensure the gesture setting is off, before re-adding your Fenix 5 to Garmin Connect Mobile.
If the problem persists after this, then send an email with the details to the email address in the first post of the beta software sticky thread. You could also raise a support ticket too, as that's your formal notification to Garmin of the issue should it eventually require further technical intervention.
