ok so I have an update. The router has crashed 3 times today and managed to get the console cable logging to see what happened before the crash and I got this
[20161122 12:08:49.248] ERROR[18816] security_events.c:1308: Failed to issue security event of type SuccessfulAuth.
2016-11-22 12:08:54 Kernel.Alert 10.80.1.1 Nov 22 12:08:55 DatalinqFirewall kernel: CPU 1 Unable to handle kernel paging request at virtual address c000000003bad008, epc == ffffffffc0a329fc, ra == 0000000000000040
So has anyone seen this before?