Cisco has raised a field notice on this issue: http://www.cisco.com/c/en/us/support/web/clock-signal.html#~field, If your unit is under warranty you are in luck, if no warranty then your out of luck.

I have had 5 of these units doing exactly the same as you mention above. they were all purchased in around 2015 so are not under warranty or smartnet. Has there been a bug raised by cisco on this?