With my old android v4.4 phone, current version of Garmin Connect in Oct 2016 and firmware v7.2, After pairing the phone to the E520, I never had to do do anything with my phone and E520 and the phone would automatically connect to the 520 and maintain a stable connection the entire ride.
Now with my new phone Xiaomi Redmi 4 Pro (Andriod v6.0.1 /MIUI 8.0.5.0) and Garmin Edge 520 firmware v11.0 I need to open the Garmin Connect software on the phone to get the Bluetooth to connect and then on top of that it only maintains a connection for around 30 minutes then disconnects. At which point I would need to go back in to Garmin Connect to reconnect.
At this point I am not sure if it is the phone/android version/setting issue, Garmin E520 firmware or Garmin Connect version that is the source of the issue so, it would be helpful to know if anyone has Bluetooth working with the current E520 firmware and connect software version in a fully automatic fashion. I would of course try my old phone, with the the E520 running the latest firmware, except my old phone is dead.
I have wiped the E520 completely, it made no difference to the issue.
As a note, I struggled to pair my phone to the E520 to my new phone in the first place. Using the procedure as described in the manual that worked in the past no longer works. If I never open the Garmin Connect Software, it will never connect.
I will try changing the application security settings on my phone to see if that will help.