@Somnus You were correct, I had to attend site, the Omada was being reset too quickly and the logs were not helping they simply stated repeating disconnects from all switches.  I reset the switches to factory so that the Omada could be removed from the problem.  Reconnected the switches one at a time noting which one caused the Draytek to crash.  Having worked out which switch was affected, removed all the patch leads and then patched one at a time until a port threw the loopback on the switch.  Located a client suppled and connected switch connected to two wall ports in the building...... hey presto culprit located.

Thanks for the advice.