You can test whether the new cbo.dtb has been flashed & picked up by CBoot by stopping at the CBoot console (press any key during boot) and typing:
printvar boot-order
That should display the boot-order CBoot is using. I would guess that you haven’t updated the CBO partition correctly if you still see the default boot-order of '“sd”, “usb”, “emmc”, “net”.
Note that the cbo.dtb file should be placed in bootloader/t186ref IIRC for flash.sh to find it.
You can also (temporarily) change boot-order at the CBoot console using setvar:
‘setvar boot-order emmc, sd, usb, net’, OR just use ‘setvar boot-order emmc’
And then enter ‘boot’, you should see CBoot go directly to ‘Fixed storage boot’
Tom