_error returning 200 on App router page

[jcole356]

We're currently receiving a large number of Invariant: expected pageData to be a string, got undefined errors thrown from base-server. I am unable to reproduce this outside of production and have no insight to the root cause.

To make matters worse, it appears that when this error occurs, Next.js seems to be returning _error with a status 200. This is getting cached in our edge due to the 200 status.

Isn't _error supposed to be a Page router concept? I was surprised to see this returned from the App router at all.

Why is it returned with status 200? Isn't returning an error page with status 200 an anti-pattern?