At first I would like to tell that DocumentURLPath != NodeAliasPath. These two can be different. Not sure if this is also the case. However, it is possible that you are calling the GetParentAliasPath() method too early or too late. So, it will not set the WHERE condition properly.
I would try loading the WHERE condition in the code behind, e.g. in the OnContentLoaded() event. And after setting the property I would also call ReloadData() on the repeater control.