Dear James,
It might be because of few reasons.
1. First, you should select Last Touch Channel as primary dimension and Last Touch Channel Details as secondary dimension. Kindly do not select Referring Domains as secondary dimension.
2. Make sure that you have selected the time period and metric properly. It should be after the change.
3. Check whether Referring Domain Rule is below the Paid Rule in Marketing Channel Processing Rules. Like below:

4. Make sure that you are using "Any" rather than "All".

Thank You
Arun