Sorry to hear that problem.
Did you formatted the HDD with uTrack24 before you started the recording?
Which firmware on your uTrack24?
Did you use any extension cable for the HDD?
The HDD external or USB powered?
When the uTrack24 does not find the song for playback usually that’s mean the write was not success. This can happens, if the drive was not able to write data on the drive. Some drives are really sensitive for the environment resonance (loud low frequency music, or any other resonance) in this case the HDD puts the heads to parking position, in this case the data transfer stops, no writing possible. Did you use any soft material below the drive?