I have good news! My bees have finally started using the flow frames.
In my last inspection, I took each of the flow frames out and smeared them with the sticky burr comb that the bees had built in the lid. This put some lovely trickles of honey and fresh wax into the flow frames.
This seems to have worked as I inspected today and found all the frames being busily worked on with some of them full and capped.