Sming fileSetContens sometimes resets ESP-WROOM-02

[KernelPanic]

I app I am working on, I am trying to save WiFi credentials on SPI Filesystem with following method:

Code: Select all

void ApplicationSettingsStorage::saveFunction(void *arguments)
{
    Serial.println("Saving settings...");

    const String json=getJson(false,
                              true); // Passwords are saved, timestamps are updated on every save.

    Serial.println(json);

    /*
     * Excluded reasons for bug:
     *     - NON-NULL Terminated String: I've explicitliy added "\0" to json variable before saving it to file,
     *                                   same result, random reset
     *     - Memory corruption:

    fileSetContent(APP_SETTINGS_FILE,
                   json);   // BUG: Here occurs random reset !!!
}   // saveFunction

Now, calling fileSetContent forces whole ESP-WROOM-02 SOMETIMES TO RESET on random occasions. Why?