If you've created a new instance of Field Service in Dynamics 365 v9 you may have a problem where the Products, Services & Service Tasks from the Incident type don't auto-populate to newly created Work Orders.
If you have an Incident Type configured with Products, Services and Service Tasks, when you create a new Work Order, if you link it to that Incident Type then these are copied down to the Work Order upon creation. However this wasn't working for me - no error, just no records appearing.
I found that the workflow behind the scenes in this environment was linked to a user who didn't exist. If I reassigned the workflow to my account (a System Administrator within the environment) then the workflow worked again. You probably need to do this for all the Field Service workflows with "--- ---" shown as the owner.
To rectify, go into Settings > Customizations > Cutomize the System and then navigate to Processes on the left. Open the workflow (one at a time sadly) and then click "Actions" from the top of the dialog and then "Assign" and assign it to your System Administrator account.
Re-trigger the workflow and observe that it works now.