Still seeing this. Currently blacklisted:

blacklisted ZX1G22KCFN
blacklisted ZX1G22KGK7

Looks like someone got to these yesterday.  But I went ahead and fixed up the device status files.  Should be green on the next run which will be https://build.chromium.org/p/chromium.perf/builders/Android%20Nexus6%20Perf%20%281%29/builds/2168

Should this be closed?

Just took a look and it was fixed until https://build.chromium.org/p/chromium.perf/builders/Android%20Nexus6%20Perf%20%281%29/builds/2198 upon which ZX1G22KGK7 was blacklisted again during the provisioning step for failure to reboot.

But that device is up and responds.  Just issued a reboot via adb and it booted up fine.  So I don't know what is going on.   

Let keeps this open as if this happens again I'll re-flash and if after that still no joy I'll replace it.

The devices have been stable.