Hi Daniel.

This 404 error shows IIS page. For the debugging purposes the recommendation is to enable PassThrough responses in IIS:
https://docs.intersystems.com/iris20242/csp/docbook/DocBook.UI.Page.cls?...

IRIS returns 404 when the page or class does not exist, and when PROTECT error happens.

So enable the PROTECT events in the Audit, and check if anything is logged there

Check that IIS is configured correctly to forward the request that returns 404 to the Web Gateway and then IRIS

expandAll does not invoke any callback methods.

It shows only the nodes that are defined currently for the tree

See for example sample page csp/samples/ZENTest.DynaTreeTest.cls

Execute zenPage.getComponentById( "tree").expandAll(true); from the Developer console. Note, that no nodes are expanded.
Now click on the Vegetable -> Fruit, then collapse them and call zenPage.getComponentById( "tree").expandAll(true); again. Now these nodes are shown. However, children for Animal and Mineral are still not shown, because they are not populated yet