For excel export reasons (see Export Data to Excel in Flattening mode for Web client ) I built a layout using the flattened presentation, with 2 entities by row (Legal Entity then Material).
Before using the flattened option, I could drill down by clicking on my Material entity.
Now that it's flattened, I can drill down by clicking on the Legal Entity, but clicking on the Material does nothing.
The ergonomics of the report is adversely impacted by the flattened presentation. It becomes less clear to the user how they can drill down.
Adding the entity as a block, hiding the flattened entity, then set up a drill on the block. But this has performance impacts, as mentioned by Antonio Speca.
When the layout is flattened, allow the default drill down by clicking on any entity by row instead of the first only.