Unable to refresh in service when appending difference datasources

Hi,

I have a test case report with two sources - one a redshift database, the other a google sheet. I want to append these together. 

This refreshes fine in desktop, but won't refresh in the service. I get a timeout error against the redshift database.

If I remove the append so that the sources are completely separate, then it refreshes in the service. This points to an issue with privacy levels, but after nearly a week of investigation I still can't resolve this.

I have both sources in desktop set to a privacy level of Public (should be Organisational, just using Public to get working):

and this is similarly matched in the service - the Google sheet is a gateway, the redshift database a direct connection:

I've tried clearing out all permissions and re-entering them in Desktop. I've tried clearing the desktop cache. I've rebuilt the report to append as new, and tried telling Power BI to ignore all Privacy levels, all to no avail. Are there any guru's out there who can suggest something I've not yet tried?

thanks

Matt