Attach (recommended) or Link to PDF file here:
https://www.placementsmondiauxsunlife.com/content/dam/sunlife/regional/canada/documents/slgi/4839-I-F.pdf

Configuration:

- Web browser and its version: 91.0a1 (2021-07-03) (64-bit)
- Operating system and its version: Windows 10

Steps to reproduce the problem:
1. enableXfa = true
2. Open form

What is the expected behavior? (add screenshot)

![image](https://user-images.githubusercontent.com/7104454/124389449-1ede2b80-dcb5-11eb-98ba-01e1f3d6c6f5.png)


What went wrong? (add screenshot)

![image](https://user-images.githubusercontent.com/7104454/124389460-2c93b100-dcb5-11eb-9768-98ddd2c8f1e7.png)

if (!templateNode.value) {
    const nodeValue = new Value({});
    templateNode[$appendChild](nodeValue);
    templateNode.value = nodeValue;
  }
  templateNode.value[$setValue](value);
}
function* getContainedChildren(node) {
  for (const child of node[$getChildren]()) {
    if (child instanceof SubformSet) {
      yield* child[$getContainedChildren]();
      continue;
    }
    yield child;
  }
}
function setTabIndex(node) {