You could try a couple of things here. First try comparing the properties as strings proper, and also casing might come into play:

@DynamicMode.AncestorsOrSelf.Last().Children.Where("level == @0", "2").First()

Nope. The only solution I've found is a workaround. But it's not ideal:

      @foreach(var node in DynamicModel.AncestorsOrSelf){
            if(node.Level==2){
            <li><a href="@node.NiceUrl">@node.pageTitle</a></li>
                foreach(var subnode in node.Children.Where("UmbracoNaviHide != @0", "True")){
             <li><a href="@subnode.NiceUrl">@subnode.pageTitle</a></li>
                }
            }
          }

I think I'm going back to v4. Too many bugs and issues

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