Odd Mashup URLs in 404 list

I’ve got this plugin installed on a couple of my sites and one of them is showing a bunch of odd 404s where the URLs consist of mashups of URLs for multiple pages on my site.

Sort of like this:

/actual-blog-post/privacy/contact-us/
/actual-blog-post/contact-us/
/another-actual-blog-post/contact-us/
/actual-blog-post/privacy/privacy/

Where:
actual-blog-post
privacy
contact-us

…are all actual pages on my site.

I’ve got a list of hundreds of 404 errors of actual page names with /contact-us/ tacked on to the end of the UFL.

Pages with those URLs don’t exist, so they’d properly generate 404 errors if someone were to search for them.

Any idea what this might be about?