Hey @joebuhlig,
I actually created PRs for the procourse-static-pages plugin recently. Glad you removed the Licensing, since I think more people can benefit from this plugin.
When I make a post, linking to a non-existing procourse-static-page, I see the same behaviour as I described. So when you click the link in the post, Discourse opens that URL and receives a 404 from the controller (as intended). However, the frontend then redirects you to /404. Meaning that if you go back, you again hit the non-existing route which again redirects you to the /404.
We’re still dealing with this problem, and I think your plugin can also benefit from a solution.
Arjen