what kind of reasons make software reset(0x04)?


We created a product using nrf52840.

the product is operating well, but it has been confirmed that software reset (0x04) operates in very few times (2weeks per 1time).
In this case, I want to know software reset due to low power or external physical interference are excluded.
Is the cause of software reset only in the firmware code?

Are there any causes worth considering from code?

In addition, a function was added to save to external memory in app_error_fault_handler , but there was no log in external memory even the software
reset after.

(we use sdk17.1.0)
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