This document explains the reason that a URL might be incorrectly redirecting to a seemingly random page on your site.
When attempting to access a link or URL on the site that no longer exists, instead of a 404 page (as expected) the user is being redirected to another page. This redirect does not exist in the Redirection plugin or in the Apache redirects file.
The reason for this is WordPress's native canonical redirect technology. When a page no longer exists, WordPress attempts to land the user at the proper "new" page by guessing where they intended to go. This occurs when the slugof the old page closely resembles that of an existing page on your site.
For reference, the slug of the page is the portion of the page URL that appears after the domain:
Example of page slug: https://sitename.wisc.edu/slug-here
Example of canonical redirect: If your old, deleted page URL was https://sitename.wisc.edu/bucky, WordPress might now redirect users to something like https://sitename.wisc.edu/bucky-badger because the slug starts with the same words and it thinks this might be the new location of the page.
Unfortunately, adding a redirect using the Redirection plugin will not override this feature. The best chance you have at stopping this behavior would be to rename the page slug for the page that you are getting redirected to. The editing option for a slug can be found directly below the title of the post or page, in the area labeled as "Permalink":