I still could not ping 9-4-8-4.
But I found that chameleon at 9-4-7-4 has no space left on device. Which is https://bugs.chromium.org/p/chromium/issues/detail?id=747841.

After removing the log file /www/logs/lighttpd.error.log, device should behave normally.

I have not seen boards that is unscreenable from the DUT.
If that board repro this issue constantly we should look into it further.

Thanks!

Oops, I mistyped earlier. The two boards are 9-4-8-3 and 9-4-7-4. 

Ok! 9-4-8-3 looks fine now.

Great, I was able to clear the logs on 9-4-8-3 to free up space. 
We were able to reset the boards and have them working normally but the problem was that they were unpingable, unsshable, and unscreenable in the first place. 

Is there a automated or remote solution so that we can avoid manually resetting? 

It is not clear what was the state of the chameleon. We can put some logic like "reboot if it can not get IP for 1 days" in chameleond, but we are not sure whether that logic will be running when this issue happens.

Did you try to connect to it through screen after the reboot ?
Hardware issue on USB serial port is one of the possible reasons.

We were able to screen into it after the manual reboot. 

Seems like the logic won't be running. Since the state is unclear, let's just be aware of this issue (I placed it in the Chameleon Debug Doc) and reopen this bug if it happens again.

This happened again with 9-4-8-1, 9-4-8-2, 9-4-8-3, 9-4-7-2, 9-4-7-4. I've asked Chromestop for additional chameleon boards to replace these five. 

Happening again with 9-4-8-1, 9-4-7-2, 9-4-7-3. Two of these boards (9-4-8-1, 9-4-7-2) failed before according to #8. Will replace these two and check the status of the other failing board in lab. 

I've replaced 9-4-8-1, 9-4-7-2, and 9-4-7-3 chameleon boards.