Scatter maps in Analytics

Hi all, 

I cannot make scatter maps in Analytics work. All I get is the below screenshot. I use primary address postcode short, primary address country in the location fields and ticket paid count in size. I filter by production season and I only ask for the top 20 postcodes to be returned (apparently scatter maps are not great with large volumes of data). Before I raise a ticket with Tessitura, has anybody made them work or do you have any ideas on what I could be doing wrong?

 

Thank you,

Thanos