bug(cdk-tree): CDK Tree can't be opened when trackBy function is used after update of datasource

[MeMeMax]

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

Angular 17 (here is the same example: https://stackblitz.com/edit/zmfrj6ks?file=src%2Fexample%2Fcdk-tree-nested-example.ts,src%2Fexample%2Fcdk-tree-nested-example.html with Angular 17)

Description

Hi, there is a bug in the Angular CDK Tree. When you update the data of the tree and a trackBy function is given to the tree, you can't interact with the tree anymore.

Reproduction

StackBlitz link: https://stackblitz.com/edit/fesfbplt?file=src%2Fexample%2Fcdk-tree-nested-children-accessor-example.html
Steps to reproduce:

1. interact with the tree (not mandatory, but you see that it works)
2. click on "changeTree" button
3. try to open the tree again => this doesn't work

Expected Behavior

Tree should be updateable and interactive after an update. I would also expect that the open state is kept when only part of the tree is changed (in the example one subtree is removed, the other persists) and a trackby function is given.

Actual Behavior

Tree is closed and not interactive anymore.

Environment

• Angular: 18/19
• CDK/Material: 18/19
• Browser(s): all
• Operating System (e.g. Windows, macOS, Ubuntu): windows

[wagnermaciel]

Potential duplicate of #11381

Edit: After investigating, it seems this is unrelated to #11381 and instead seems to be a weird interaction between trackBy and expansion