DroneCAN via MAVLink doesnt work over serial

I am having an issue where DroneCAN MAVLink pass-through seemingly works over my autopilot’s USB port but only half works over MAVLink-enabled serial ports (I see node IDs but no names or other data). Is this intended, a bug, or something I am doing wrong? I see the following when connected to the FMU via a serial port and mission planner:

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