Device was failing to boot due to a low battery. Looks like it's charging just off the embed usb port on the host. It would likely benefit from a high-power USB hub. Going to charge the device offline, and connect up a hub for future stability. 

List of devices attached
00bc9aad38a6c295	device

Going to keep an eye on subsequent builds.

Device seems to be stuck in boot-loop now. Hardware is probably failing. Going to source a replacement. 

Device swapped

List of devices attached
01029a898168bc63	device

Seeing lots of subsequent green.

Along this topic, I think we need to pad out the luci.flex.ci pool with a few more of the same bots to increase duplication and capacity. JohnW, I'll file a new bug for this under Infra>Labs. Will you be able to help with this? Thanks!