Hi Jon Andoni,
Thank you for contacting Syncfusion support.
We have looked into the reported query “getNode & updateNode methods don’t work unless parent node is not expanded” and we would let you know that as per our current behavior, our TreeView component render based on the load-on-demand concepts. So, the child nodes are rendered only on demand i.e. on expanding node by clicking expand icon or double-clicking parent node.
For your scenario, you have tried to get or update the node which is not rendered in TreeView. So, we suggest you to perform your action after node expanded by using client-side event.
However, we have already planned to provide the option for disable the load-on-demand in TreeView. We have considered this as a feature and added it into our feature request list. This will be estimated to be available in our Essential Studio 2018 Volume 4 release which is expected to be rolled out in the month of December, 2018.