Dear @kristian.fischer ,
Firstly, Do you have access to Aurix via minicom and able to issue any command? If so, can you share the complete log on aurix after serial connection and hard reboot?
Also, Is tegra accessible via serial console? If so, please share the boot log.
Just double checking, Please confirm if host is connected to target’s debug USB port and left Type -C.
This confirm board is able to entering recovery mode. If you can enter commands on aurix console, please put the board in normal mode(tegrarecovery x1 off & tegrareset x1) before attempt to flash.
This error indicates either connections are not correct or other serial connections are open to target. Please hard reboot both host and target.