Checking pycom micropython source I see, that you are not useing the esp-idf functions for performing the update .... so no danger of corrupting the ota_0 slot. Still I wonder why you are doing "your one thing" instead of using the esp-idf functions ... (https://github.com/pycom/pycom-micropython-sigfox/blob/83e2f7f59e28d726a5a1d79377a5ec37f9e0065b/esp32/ftp/updater.c)