Scrollbar is not visible when items are expanded by default

[0x90d]

Using HierarchicalTreeDataGridSource bound to an AvaloniaList without recycling, setting the isExpandedSelector to a property which is true by default and displaying for example two nodes with lots of children. The scrollbar isn't visible when application launches and mouse wheel doesn't scroll as well. I have to collapse & expand a node for it to appear. The video starts with application launched.

This does not happen when the list is set/changed after the TreeDataGrid showed up.

2025-08-22.105401.mp4