If I understand well, what can happen is that the contents of the HTML control exceeds the control height, so, it's placed out of the control, causing that other controls below the HTML control don't appear as expected. If this is what happen, the solution is to use an "overflow-y" CSS rule (set it to "auto") for the HTML control, so their contents are shown using a scroll if needed, but, never exceeds the control height.
Take a look at the below sample app, copy the code and save it into a "MyApp.ab" file, for example:
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