Kronos as audio interface routing to assignable output

[Canoehead]

Good Morning,

I am using the Kronos 2 as the audio interface for my old Macbook (OS 10.5). Kronos operating system and firmware up to date.

Here is the physical routing info:

Studiologic VMK organ controlling VB3 via USB,
Audio from Mac to Kronos via another USB,
Left and right and assignable 1 audio out of Kronos to Mackie mixer.

When USB audio in Kronos is assigned to L/R everything works as it should.
When USB audio in Kronos is assigned to assignable out 1, no audio is sent to the mixer. The input meters on the Kronos do indicate that audio is coming from the Mac.

Assignable out works for other combis so not a physical problem with the jack.

Any insight would be greatly appreciated.

Thanks,
Gord