The cause of the crash was that the active_menu_ variable was set to UNIT_FACING after the unit facing setting is finished. When clicking the menu it was looking for a unit because of the value of the active_menu_ variable and on line 670 the assert failed because it could not find one. Setting active_menu_ to MAP after the unit facing is set fixes this.

src/editor/controller/editor_controller.cpp

@@ -770,6 +770,7 @@ bool editor_controller::do_execute_command(const hotkey::ui_command& cmd, bool p
 					assert(un != get_current_map_context().units().end());
 					un->set_facing(map_location::direction(index));
 					un->anim_comp().set_standing();
+					active_menu_ = MAP;
 					return true;
 				}
 			}