TYPO3 Core

currently a new tree logic is work in progress, we will not fix this issue with the current tree implementation.

The problem is not located in UserSettingsController::addToList as expected. If anyone find a simple fix, we can implement it, but at the moment we don't see a simple fix.

in version 8 saving of the tree state for categories was dropped.
The usability of this feature was questionable - settings ware saved independently for each record.
So you see the saved state backend user would need to visit the same record again.
Additionally if user clicked "expand all" all nodes ids were saved into session, making the session size grow over time.