Object is "null" when form is rendered in HTML

My problem is that there are certain objects in my form (subforms, text fields and radio buttons) which, when rendered in HTML, xfa.resolveNode returns "null" and so cannot have their properties set to the required values.

The form is made up of a few subforms which consitute the main sections. Two of those subforms return null when I use xfa.resolveNode. Then, there are a number of objects such as text and radio buttons which I cannot access for the same reason. They return "null".

I would like to point out the same form works fine when previewed as a PDF in LC which is why I am so confused! What could make HTML have trouble resolving those objects? Are there any special requirements?

Any help would be greatly appreciated.

Thanks