Carrier preference not working with bypass routing and rating

In my Advanced Preference Schedule I have set up the Transportation Preferences CUSFRT, MOT and CARRIER. For all three preferences I use the hierarchy all customers all items. The CUSFRT preference defaults the Freight Handling Code BRR. We do not use Transportation Routes and Rates. The MOT preference defaults the code S (Standard).

The CARRIER preference has the flag Include/Exclude set to I and has the field Preferred Carrier 1 populated, but in the shipment, the carrier field remains blank.

In the Shipment, Freight Handling Code BRR and MOT = S default correctly. However, the Carrier remains blank. Without a carrier, I cannot approve or confirm the shipment. Does anybody know why the CARRIER preference might not be working and what I should check? Thanks.