Broken links in webpages that don't exist

Hi,

I BLC is showing bad links but does not show a page in the “source” column. The status for the links is 404 error. It does show “link text” though. When I click unlink or recheck I get an error box that says
“The following error(s) occured :
* Nothing to update
* Nothing to update”

Any ideas why this is happening?

https://wordpress.org/plugins/broken-link-checker/