

It looks like you’re relying on media automounting to access the drive, but this is happening too late for Docker.
I would suggest creating the empty folder and explicitly adding the mount to /etc/fstab
instead. This should mount early enough, and even if it doesn’t it needs an empty folder for the mount point anyway.
Edit: Make sure you reference the partition by UUID, because the device name of USB devices sometimes change after a reboot.
Why shouldn’t it think that 0 is an even number? It’s divisible by 2.