Fear not! I too went through this process
1) After the failure, disconnect the dac
2) Make sure that you use task manager to kill the task of it still open - also kill tidal and any app possibly trying to use the DAC
3) Reconnect the DAC
4) re launch the firmware updated and re apply the firmware update
5) it should take at 7.2
I had to repeat this process for testing both cookies and cream and the GTO filter.
1.5 appears to be default firmware in the event that the device resets itself. As best as I can tell, the initial firmware push appears to cause the device to think it’s been “reset” as opposed to actually applying the firmware update