The vivoactive 3 or the Edge 1030 will not transfer data to Garmin Connect without the Garmin Connect application being open or open in the background.
Hopefully I have a solution for the Bluetooth issue:
You have to go to the developer options from you mobile and check this button: 'Disable absolute volume' under the Bluetooth options.
Since…
I frequently see "Phone disconnected" and then some while later "Phone connected" messages while riding. My phone (Pixel 2, Android 9) and 1030 are a few inches apart from each other on the handlebars. Happens more often on the bike where I also have a shifting sensor (SRAM eTap) connected, but I've seen it on my other bikes where there are no sensors connected.
The problem still happens with the current 4.19.1 version of GCM Android, and and happened with older versions as well. Still happens with the latest 7.40 FW for the 1030.