Nested layers are not visible or attainable from side bar

In a data table there are some deeply nested tables that I cannot access to edit…they disappear in limited width of sidebar as you can see on screenshot

There is no bug here. You can still expand the panel manually by dragging its right border. But you can only expand the Layers panel up to a certain point, so I recommend you vote up this feature request: Expand/Horizontal scroll the layers/libraries panel.