Page Not found errors experienced by users

We are seeing several users encountering Page Not Found errors because they are trying to access url/wp-content/plugins/iframe-popup/inc/blank.gif from pages on the site that do not have any pop ups set.

I have not been able to replicate the issue, but our logs definitely how that the page is being accessed. Any idea what might be causing this?

https://ww.wp.xz.cn/plugins/iframe-popup/