There are examples such as these:
https://developers.arcgis.com/javascript/latest/sample-code/featurereduction-binning-polylines/
https://developers.arcgis.com/javascript/latest/sample-code/featurereduction-cluster-polygons/
where you see the expanded widgets flashing and appearing to be expanded by default before being closed. Is this something that can be resolved?
You can try adding the stylesheet for the components. At the moment it only hides components that have not been loaded, but this might help with the flickering.
<link rel="stylesheet" href="https://js.arcgis.com/map-components/4.32/arcgis-map-components.css" />