Hello there,
There may be multiple causes for this. I think we’d have to look at your code to get a better idea. Can you upload it? If you don’t feel comfortable here I can reach out via email and get it directly.
Just as a quick suggestion, if the source file is a DWG file, perhaps you can load it in Autodesk TrueView (as a way to confirm how the Sheet in question is expected to render).