By default, the bootloader is not included in any SWU package. To include the bootloader artifacts in the update package so they are programmed during installation, set the SWUPDATE_UBOOTIMG variable in your project’s conf/local.conf configuration file to true:

conf/local.conf
SWUPDATE_UBOOTIMG = "true"
Updating the bootloader is a critical operation. Make sure the bootloader has been verified to boot properly before using an SWU package to update it, especially if doing a remote update.