Not sure what to think about this drama but I'm not even attempting another IBD with my limited Internet until I learn how to backup my copy of the blockchain somewhere for when my node craps the bed. StartOS backup apparently doesn't include that data, and not sure if there's even an option to tell it to.
Discussion
It's not a built-in option of StartOS, but since it allows access over SSH, you can upload/download whatever you want using ssh or scp. You'll have to know your way around linux and the StartOS filesystem structure.
Here is some documentation to migrate the blockchain TO startos: https://docs.start9.com/0.3.5.x/service-guides/bitcoin/blockchain-copy#blockchain-copy
(you'll have to do the reverse when you want to copy it from startos to another machine)