You would've needed to have removed all partitions, so you did that correctly. The older Debian build and Manjaro are quite different, and use different variations of the bootloader. That could've cause problems if you didn't.
When attempting to boot into the SD card what is the PBPs behavior?
If your problems are persistent you can boot from SD by removing the back panel, using the switch to disable the eMMC, boot from the SD, and if you'd like to use the SD to reformat your eMMC you have about 1 minute to flip the switch and re enable the eMMC when booting from your SD. I believe there may be some commands that could rebind if your OS is already booted, but I cannot recall them, and they haven't been added to the wiki yet.
When attempting to boot into the SD card what is the PBPs behavior?
If your problems are persistent you can boot from SD by removing the back panel, using the switch to disable the eMMC, boot from the SD, and if you'd like to use the SD to reformat your eMMC you have about 1 minute to flip the switch and re enable the eMMC when booting from your SD. I believe there may be some commands that could rebind if your OS is already booted, but I cannot recall them, and they haven't been added to the wiki yet.