Thanks for the clarification.
Our analyze shows that your HTML uses some Javascript which displays some elements if they are in the current viewport. The feature was probably added to your code recently. The viewport height is set to the page height minus margins so your JS code thinks that the window is small (e.g. 600px).
You use the Domain License so the only solution it to remove such Javascript from your code.
The alternative is to migrate your code to our API. The API has option
setViewportHeight. If it's set e.g. to 16000, the PDF is fine.