MCUBoot reverting slots immediately after image swap

Question

Hi, 
 OS: sdk-nRF 2.3.0 
 OTA slots: primary slot 0 on the uC; secondary slot 1 on external flash 
 Chip: nrf52840 
 Build OS: MacOs 
 Problem 
 We are using LwM2M to perform DFU which has been working fine until recently when we tweaked the partition locations. Aka we moved the settings partition to the end of flash (primary) and made it larger in size. 
 The firmware runs fine when flashing the "merged.hex" file. 
 When we perform a DFU the download to slot 1 goes fine. When executing the update MCUBoot swaps the content of slot 0 for 1 as expected. However as soon as this finishes it then reverts the slots back, see image below. 
 
 I'm lost as to why MCUBoot would revert the slots before the app as even attempted to load. 
 
 Debugging 
 In the past MCUBoot would load as such, with no secondary reboot/reverting.

I've also noticed when doing a "sys_boot()" the uC will actually reboot twice; which does not seem right. 
 
 However when boot the device up from cold / real world power cycle, it only reboots once: 
 
 The paritition.yml file can be seen here encase it helps: https://gist.github.com/motters/072ffe54c56c074a3fd96e907b973999 
 
 Let me know if i can provide anything else that will help. 
 
 Any help greatly appreciated. 
 
 Thanks, 
 
 Sam

motters · Accepted Answer

After a 2 days of messing around with dfu issues i may have fixed it. I have no idea why but the following seem to be required: 
 In mcuboot prj.conf 
 
 Removal of CONFIG_PM_OVERRIDE_EXTERNAL_DRIVER_CHECK=y 
 Add in CONFIG_BOOT_WATCHDOG_FEED=y 
 
 In app prj.cong 
 
 Add CONFIG_ROM_START_OFFSET=0x200 
 Removal of CONFIG_PM_OVERRIDE_EXTERNAL_DRIVER_CHECK=y

Not sure which 1,2 or 3 fixes it. But want to update the thread. 
 
 On sys_reboot is now only does it once 
 
 Any executing the update only swaps slot data once

MCUBoot reverting slots immediately after image swap

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