Most of the time, beacons transmit and the receiving software such as apps on iOS and Android or applications on single board computers (SBC) only read the advertising data. There’s no connection to the beacon. However, for programmatic setup of beacon parameters or accessing some sensor data, applications might need to connect via Bluetooth GATT.
There’s a recent article on How to Work Properly With BT LE On Android. It provides some useful pointers such as not performing scanning and GATT connection simultaneously, avoiding auto-connect and not blocking GATT callbacks.
GATT can be flaky on Android. While scanning for advertising data usually works well, we have found that GATT connections fail all the time on about 5% of devices. This is due to poorly implemented OS Bluetooth software. This means beacon manufacturer-supplied configuration apps can’t connect. The only solution is to use a different phone (or the iOS version of the app on iPhone).