The trouble is the “undisclosed loans” weren’t undisclosed: they were disclosed in filings during the primary when they were taken out, but not during the general because there was no statutory requirement to re-disclose them. We’ve had posts here at FR showing copies of the disclosure documents.
You might not understand. Look up why it’s so important to disclose and obey FEC regulations election finance law. It’s to avoid outside influences bankrolling candidates. And it certainly looks here that this is a real possibility of what occurred.