when using secureDFU with sdk12.2, only changed the mac address. my application is more than 60KByte, when i test the firmware for two files, one is 62K and an other is 64K. it got a trouble, when data send througth finish.and bootloader reboot.
it still remains some contents in swap region. try readback the flash what in application and swap region fond it. and s_dfu_settings told it's already finish.
re-send the zip file with nrf connect it will be allright. I'm trying to trace and found what is going wrong. maybe try using the default bootloader without any change。
founded and it's made by me wdt.
when Copy the application down safely app_sched_execute is never called