Got a response, they do not know what is causing the issue. Will post any updates, but I think @Graphite's solution is probably best for now.
Subject: Possible reason for mobile access issues
Your Message 05/08/2023:
As of the latest Android app update (April 13 -- version 6.22.0), the app fails to load on my phone. I have a theory that this is because I am running GrapheneOS, a secure operating system that is not certified by Google. Several others have reported the same issue with the same operating system. Are you able to confirm whether this is intentional behavior, or a bug?
Some banking apps do intentionally prevent themselves from running on nonstandard operating systems, so I wanted to check if that is what is happening.
Thank you for your time.
Navy Federal Response 05/09/2023 :
Thank you for using Navy Federal's eMessaging Service, Ms. XXXX. Please accept our apologies for any inconvenience and frustration this incident may have caused. Upon review of your account, we show that a ticket was submitted for investigation into this issue for you, ticket # 51300. They are still investigating the issue, so we are unable to speculate on what the issue actually is. If you have further questions, please let us know.