In previous releases of Revit we have been able to automatically place ceilings in rooms in most instances. In 2017 the reasons for not being able to place rooms automatically have changed. In my opinion this should be considered a bug.
The situation I am referring to is when we have a room that has a wall protruding into it, (see image below). Prior to Revit 2017 a ceiling would go into this room with out any problem. Now in 2017 you will have to manually place the ceiling using sketch lines.