In FCP, the bottom filter acts on the one above it. I never use FCP’s keyer so don’t know its vagaries. The Primatte keyer in Motion is excellent. That might have worked better for you. Another approach might be to export the FCP-keyed layer using the Animation codec to preserve the alpha channel, and then put your supression CC on that after importing it and replacing the original track, although, that’s probably as time consuming as the method you described.
John
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