Deprecated Warning Widget.widgets is deprecated

[lp9052]

I got following warning when running pytest:
reacton\core.py:362: DeprecationWarning: Widget.widgets is deprecated.
before = set(widgets.Widget.widgets)
reacton\core.py:1936: DeprecationWarning: Widget.widgets is deprecated.
orphan_widgets = set([widgets.Widget.widgets[k] for k in orphan_ids])

All occurrences of referencing Widget.widgets throw DeprecationWarning.

In ipywidgets(8.0.6), it states:
# Because this is a static attribute, it will be accessed when initializing this class. In that case, since a user
# did not explicitly try to use this attribute, we do not want to throw a deprecation warning.
# So we check if the thing calling this static property is one of the known initialization functions in traitlets.

Anyway to avoid?

P.S.
What's the difference between render() and render_fixed()? I do see render add another container around elements. Any explanations about when to choose which?

Thanks a lot.