Hi,
I may not have been clear. I let Teltonika Configurator to do whatever it wants, without interrupting. For example, I start the update, go to have lunch, back in 45 minutes. Though the device is blinking normally, it still has the old firmware version. (Just as one would expect after the "Update failed" message right before "Could not reach device" one.)
It's appr. 15 minutes in the fast blinking state before reverting to normal blinking and appearing as a COM: port.
I'm not updating the firmware just for fun. The BLE configuration features (like sending the beacon MAC address that is printed on the beacon instead of the internal 16-byte ID no one can tell) require a newer firmware.
A BLE firmware update could be also nice - if the update file to be uploaded was available anywhere.