Refresh to Datamart from Power query not working

So I have a created a datamart. It uses a on prem SQL Server as it's soure, in which I have built a simple star schema. I can connect, load my data, transform it, model it, report on it. All Great.

However if the data changes in the SQL Server i want the datamart to refresh. I open the datamart and if I hit refresh nothing happens. I can go to transform data, and press refresh in power query and I see the correct data that is in the fact table. However if I then hit save the datamart does not update. In the loading data phase it simply says 0 rows and nothing in the datamart changes.

I even took out all the rows from the Fact table, and this is reflected in power query, but again does not pull through to the datamart.

If i change the schema of the fact table, or add a custom column, then the refresh works. So it is clearly not a connection issue. It somehow does not seem to recognise that the data has changed. Of course I do not want front end users having to go in and create/delete a column eveyr time they want the data to refresh.

Any Ideas?