Could you please test using a simple SQL statement? You can create a simple table named TableA in your database, then type the basic query statement using like: select * from TableA in Direct Query model, check if it works. Some function is not used in Direct Query model. If it works fine, it will document the function is unable. You'd better test step by step.
If the function is not used, please create a new result table, then import them to Power BI. If you have any issue, please let me know.
We've just hit this issue in one of our databases. Its accessing a TABLE.
The table is using user defined data types!
A copy of the table using the underlying SQL SERVER types wokrs fine. The user has data_reader and public roles/permisisons
To give them appropriate access you need to give then VIEW DEFINITION permissions so the DB can resolve the undelrying schema shenanigins into some normal looking datatypes that PowerQuery can get its head around
GRANT VIEW DEFINITION TO TestUser;m
if you have lots of users or are using groups/roles you can grant VIEW DEFINITION to the public role of the DB assuming you're happy with the security implications.
Having similiar issue. When I call a view from a function, I get the 'transformation' error. When I call the view directly I get zero issues. When I call the function with the query from the view in it (Table valued function) I get zero problems. Not doing any transformations so this seems to be a misleading error. Anyway, my work around is embed the view query in the function.
( Ihave to report to a log who viewed what when, the TVF is my only route to use PowerBi given the security requirements. and it has to be direct query until I can refresh imported data more than once a day.