After OSUpdate device not booting from slot B even after marking

set-active=a if you have slot B active or fastboot --set-active=b if you have slot A active Check the active slot with fastboot getvar all

Super Partition Dynamic Partition A & AB Slots Fastboot Detailed Guide munchy•55K

fastboot get active slot Get the current active boot slot: fastboot getvar current-slot fastboot --set-active=b Great if its just a command error, else this

fastboot getvar currentslot try setting the slots again, without the space between -- It will return fastboot --set-active:a fastboot: unknown option – set-active:a