This tool can read current or change default HCI_LE_AUTOCONN_TIMEOUT value for Bluetooth adapter on Linux. The default value is defined for the kernel 5.15 at include/net/bluetooth/hci.h:
#define HCI_LE_AUTOCONN_TIMEOUT msecs_to_jiffies(4000) /* 4 seconds */and it can be too low if the advertising interval for a device is high (for power saving).
You can also change the value in /etc/bluetooth/main.conf, line LEAutoconnecttimeout. The value in ms and will be applied at boot or when bluetooth service is restarted.
The tool changes timeout to hardcoded value 16000ms. You can change value NEW_LE_AUTOCONN_TIMEOUT in the lower source file to required value .