In this article, Customizing Status Icons for Community Posts, we've been shown how to change the status of posts that displays to end-users to something custom and is fitting to our product and culture.

I used the same logic to also change the status selector for agents and admins.  It turns out that this logic, although working, isn't supposed to be allowed and recently it broke the Community Post page in my theme and many others as well.

Here's the explanation from support:

Just heard back from our devs. It sounds like they made a change which led to the 500 errors you (and others) were seeing, and then they promptly reverted it. That's why things are working now. They let me know that the errors were related to using post.actions in a conditional. That's theoretically not allowed, since post.actions is a helper and not an object, but there was no validation around this, so it was allowed to go through (and work) until now.

The devs recommend that you move away from using conditionals like this, since it's something they are looking to start enforcing in the future.

So, in the future at some point, we will be able to modify the visible post.status, but not post.action for the menu that agents and admins use to update the statuses.  

If a custom status is being used for end-user communication, it would make sense for agents to use the same list when they are making updates.