Certainly nuLink 23xx does use Updater.exe in preboot. If the screen of the device isn't held for long enough then the preboot connection might be dropped but that's not what seems is happening in your case. Usually holding until "Updater"/"Software Updating" appears on the device screen is sufficient however holding for the entire process is best to be sure. Once a flash is initiated it should complete in the case of a 'soft-bricking'.

A faulty region in the device memory or a physically failed chip can be a cause of the flash not completing.

So, provided you're sure the RGN file has been properly prepared and your flashing procedure is correct, there may indeed be a hardware fail. Do you get a "success" message or any any other message on screen after the 100% green bar?