Since the upgrade toward AI CC 2019, in the Layer Panel, the layer automatically unrolls to show the subkayer in which the selected objet is. When another object in another layer is selected, the layer unrolls too and the first layer stays unrolled.
According to the support, this is the new feature to make the use smoother. I would have to disagree on that and it would be nice to be able to disable that automatic unroll since it makes the use of the layers panel very complicated.

From what I recall, this feature was not part of the older version (AI CC 2018 for example) and using the layer panel was easier because we could see the sublayers only if wanted.