HI Mark,
The OOTB incident process has a condition that checks if the category has been set. If no category is set the assumption is made that it was not raised directly with an analyst but via Self Service or Email, for example. The incident is OOTB also assigned to the support group that is held against the raise users location. So if you don't have a support group associated to the location that is then in turn has users associated you will end up with a NULL assignment.
You should be able to see this if you open the relevant incident process within Process Designer in Console. It will look something like this:
What you need is an assignment after the Yes branch of the 'Category Set?' condition that assigns to the Service Desk. You can do this by deactivating the process and adding an assignment 'arrow' onto your diagram. Set the group to be 'Service Desk' and join it up as required. Here is an example of another incident process. This doesn't use the 'Category Set?' condition but it will at least give you an idea.
