Hmm. We have not used Yoast Pro, only the free version. So that may not be our issue. When I use the Redirect Tester via the support page, I get this message:
HTTP 302 Found - The resource has temporarily been moved to another location. This is superseded by 303 and 307.
URL is not being redirected with Redirection
Target: https://iac.mdschoolconstruction.org/index.php
In Redirection, source URL /wp-content/uploads/2021/01/FIN-Original-APG-Revised-8-20-20-1.pdf is set to redirect to target URL https://iac.mdschoolconstruction.org/wp-content/uploads/2021/09/APG-Revised-9.14.2021.pdf using a 301 code. So it appears that something is changing the target from what I set in Redirection.