Restart during sleep on Elitebook 855 G7

[JayBlackwood]

I've just got a new laptop and when the systems sleeps it often restarts itself.  From the Event Viewer I see two items every time it does this:

• Kernel-Power,  Event  ID 41, Task Category (63), "The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly."
• EventLog, Event ID 6008, "The previous system shutdown at <time> on ‎<date> was unexpected."

Summary of the status and things I've done:

• System is powered during sleep (connect to HP USB C doc).  
  • I've seen at least one case where it did not reboot while only on battery power (need to try to confirm that again)
• The restart is not due to software updates. 
• I've updated Windows and all the drivers I can think of. 
  • We actually tried two different versions of Windows and see the same issue.  
• The BIOS has been updated to the latest. 
• A co-worker of mine got the same system on the same day and is experiencing the same problem so this is not likely to be a hardware issue.  I've also run the extensive HP Hardware Diagnostics and they pass. 
• "Turn on fast startup" is turned off.  
• System does not restart while hibernating (no real surprise there)
• System does not restart if sleep is turned off and system left to run
• System works fine with the exception of this restart issue - so no other obvious issues.

Any hints on how to diagnose the issue or what the issue might be?

[JayBlackwood]

Just an addition to the symptoms:

• No restarts seem to happen while under battery only  (overnight test)
• System restarts while sleeping and connected to external power supply (not the USB dock).