If you use avidemux2_cli.exe, then you are already implying --nogui. Do not use that option with the cli.
If you use avidemux2.exe, it is the gui. Adding --nogui like you did would be right in that case.
I don't know about Jan, but I am confused by your title. Are you saying there is an Avidemux checkbox or menu option in the GUI or flag somewhere to "shutdown after processing"?
What I do know is this, and Jan guessed the same thing: When you are doing a lot of intensive computing and your computer randomly and spontaneously reboots without any reason, this is a classic example of a hardware failure, meaning bad memory, inadequate cooling, or a bad power supply. On the other hand, if the Operating system pops up a General Protection Fault (GPF) complaining that Avidemux crashed, that is a software failure. If the Operating System itself crashes into a Blue Screen of Death (BSOD), that is also a software failure in the OS itself, likely due to an old video driver or audio driver, but it very low level that failure, between the OS and the hardware.
It's hard for us to explain things to each other due to language differences at times, but I think this is what you are describing. If not, please be more specific.