lastvalue not updating when setting up UPSERT

I'm using Workbench 5 to set up some new datasets, on transactional tables which are updated often.

I'm testing this on a simple example, and have followed the guides https://knowledge.domo.com/Connect/Connecting_to_Data_Using_Workbench_5/Using_Upsert_in_Workbench_5 , Section How Do I Change Data Capture in https://knowledge.domo.com/Connect/Connecting_to_Data_Using_Workbench_5/13Workbench_5_FAQs and also from this post https://dojo.domo.com/t5/Workbench/How-do-I-use-lastvalue-variable-in-workbench-4/m-p/9244#M188

My query is set as this:

select id, last_updated, skills
from domo_test
where last_updated > !{lastvalue:last_updated}!
order by last_updated

I created the dataset using an initial value last_updated  as to_Date('01/01/2015','dd/mm/yyyy')   as the per the documentation. Once loaded, I changed the Update Method to Append, and selected the ID as my Upsert key on the schema tab.

When I run the job, there is no change in the query -  I cannot see any change to the variable , it remains with the intial date set, and continues to load the same query with the intial date.

Using the solution in  https://dojo.domo.com/t5/Workbench/How-do-I-use-lastvalue-variable-in-workbench-4/m-p/9244#M188 also does not work - if I set the value of the variable to  !{lastvalue:last_updated}! and run the job it ends up in an infinite loop.

How is the lastvalue variable set, and can this be seen anywhere in Workbench?