MGMT_DEBUG=1 /usr/local/libexec/bluetooth/bluetoothd -n -d -f /etc/bluetooth/main.conf

Not possible to enable continuous BLE discovery: BLE discovery works for 10 seconds, then it waits 5 second and start again.

adapter.c

#define IDLE_DISCOV_TIMEOUT (5)
...
/*
 * In case the restart of the discovery failed, then just trigger
 * it for the next idle timeout again.
 */
trigger_start_discovery(adapter, IDLE_DISCOV_TIMEOUT * 2);

...
if (adapter->no_scan_restart_delay)
	trigger_start_discovery(adapter, 0);
else
	trigger_start_discovery(adapter, IDLE_DISCOV_TIMEOUT);
break;

There is a condition in Bluez, to restart discovery immediatelly (without 5 second idle), when Discovery Filter is set.