One scenario missed in the list of causes is a corrupted runtime image. An advanced topic is enabling support for the watchdog in your bootloader and having a

One scenario missed in the list of causes is a corrupted runtime image. An advanced topic is enabling support for the watchdog in your bootloader and having a defined recovery path when the system fails to load or, worse, the application falls into a boot loop. If you have the space, you can fall back to a recovery image or duplicate of the application. If you don’t have the space, falling into a DFU mode is a good plan.