In release 20.10.10 of the UIExplorer e.g. the hierarchy of buttons in the toolbar is displayed correctly.
Since release 21.4.3 until the current release the hierarchy is displayed incorrectly.
The structure can be opened infinitely and repeatable.
I assume there is an error in the algorithm when building the visual representation of the hierarchy tree. This error also occurs with other elements, e.g. the scroll bar.