Hello ,
Below is information from SE, you can refer to:
"
The root cause is the command should use "-n" parameter.
The tool always exits from debug mailbox after successful authentication when “--no-exit” parameter is not used. But when you need to execute “enter ISP” command, you should not exit the mailbox to remain in authenticated state.

nxpdebugmbox -p 1.0 auth -b 0 -c dck.dc -k dck.pem -n
Also, need "-n" for "Enter ISP Mode", this avoid the reset and keep the debug permission.

nxpdebugmbox -n -p 1.0 ispmode -m 1
"
BR
Alice