Hi @thewake,
I'd like to suggest you refer to following document to know about power bi data refresh.
In addition, you can also take a look at following link which mention similar things.
Regards,
Xiaoxin Sheng
HI @thewake,
In fact, on premise gateway also support mixed data source, but it has some limitation on it.
You can refer to below link to turn on this option to use on premise gateway to handle cloud service:
The On-premises data gateway enables you to merge or append on-premises and cloud data sources in the same query.
Merge or append on-premises and cloud data sources
You can't do advanced operation on mixed data sources(append, merge, combine, reference other query, invoke custom function), or it will failed to refresh.
Regards,
Xiaoxin Sheng