Link to view inside subfolder does not display correctly

It has to do with the way CI handles URL's, namely in segments.
The first segment is the controller.
The seconde segment is the method inside that controller
All subsequent segments are parameters for the method.

So, the url "page/view/item-2/subitem-1" has 2 parameters, where your view method is expecting only one.
You should find a way to combine the segments that follow after segment 2.
See documentation about the URI class.