01_walnut cell with two islicer commands only renders one islicer

[lauramurgatroyd]

This happens irrespective of the ipywidgets version

[lauramurgatroyd]

A later cell which uses link_islicer to display and link two islicers displays them both fine

[lauramurgatroyd]

Same behaviour with VSCode+ipywidgets 7.8 and Jupyterlab + ipywidgets 8.1.2