If this uses a non-dev kit carrier board, then the device tree used by the default dev kit JetPack/SDKM will be incorrect. You’ll need to use the software provided by that carrier board manufacturer (which will be almost identical to the dev kit JetPack/SDKM).
Btw, the recovery button has no requirement to hold it down for a few seconds. If the button was held either at the moment of power up or power reset, then you can let go immediately.
One possibility of having flashed the wrong device tree would be that of failure of USB ports or ethernet.
Also note that once you run any operation on a recovery mode Jetson that you must restart recovery mode for any new operation. For example, you cannot flash twice in a row, nor could you clone twice in a row, without restarting recovery mode. The Jetson would be starting in a bad state if two operations are attempted in a row.