When walls intersect, Revit creates a butt join by default and cleans up the display in plan view by removing visible edges between the walls and their corresponding component layers. The view’s Wall Join Display instance property controls whether the cleanup applies to all wall types or only to walls of the same type.
Butt join with and without cleanup at fine level of detail
You can change how the join displays in a plan view by selecting a different join option (Miter or Square-off) or by specifying which one of the walls butts up or squares off against the others. You can also specify whether the join cleans up, does not clean up, or cleans up according to the default setting for the view.