When you make a BVLOS flight in an area with weak 4G signal. Disconnection between UAV and Ground Control Station may occur. XBLink will automatically reconnect to the nearest 4G base station (4G mobile tower).
If you flight in an area not covered 4G signal, UAVs return (RTL) is necessary. So, the best way to achieve safe flight is to activate GCS Failsafe on your UAVs.
The Ground Station Control (GCS) failsafe controls how UAVs will behave if contact with the GCS is lost. The GCS failsafe monitors the time since the last MAVLink heartbeat from the GCS. If no heartbeat is received FS_GCS_TIMEOUT seconds (Default seconds), the GCS failsafe event will trigger based on your parameter settings. Note that if no GCS is ever connected, the GCS failsafe will remain inactive regardless of parameter settings.
Please read the Ardupilot documentation carefully to activate GCS Failsafe
FS_GCS_ENABLE = 1 (Ground Station Failsafe Enable, switch the copter to RTL Mode. If the GPS position is not usable, the copter will change to Land Mode instead.)
FS_GCS_TIMEOUT = 35 (Timeout before triggering the GCS failsafe. 35 seconds is the time to reconect or restart the 4G module in XBLink)
FS_GCS_ENABL = 1 (GCS failsafe enable)
FS_LONG_TIMEOUT = 35 (he time in seconds that a failsafe condition has to persist before a long failsafe event will occur. 35 seconds is the time to reconect or restart the 4G module in XBLink)
FS_LONG_ACTN = 1 (ReturnToLaunch)