Custom Field causing issues with site

Hey. I'm using custom fields to have sources for our articles. The issue is, if a source is not defined, the page does not load anything past it, including my money-earning ads! We have around 1800 articles that don't have a source, usually stuff we covered ourselves etc, and some of these are our highest viewed pages.

You can see what I mean by viewing this article that does have a source:

And here is one where the source was just added as text, and not through the custom field.

I have thought of two solutions.

All of these issues are in the "Articles" category, so I could make it so this custom field does not appear in that category?

Another solution could be to ammend the code so that it is able to load the content past it even if a "source" has not been defined.

Let me know if you can help with this issue.

Thanks a lot