Comment 4 for bug 1750519

Note, that the logs you pasted were not in the logs attached; they appear to be different issues. Namely, the description:

Stdout: Invalid number 0 of holding devices: "[]"
        An error occured handling 'bcache0': ValueError - Invalid number 0 of holding devices: "[]"

Indicates a make-bcache failure; the kernel did not bind a backing device to a bcacheN device. This is also likely related to bcache over RAID5.