GitLab Pages default 404 response sends incorrect content-type header

Description of the problem

The GitLab Pages (https://pages.gitlab.io/) default 404 responses are sent with an incorrect Content-Type header. The expected header is text/html but instead text/plain is being sent. This causes the responses to show the HTML source of the default 404 page instead of rendering it within the browser.

Which Group/Project (with full path) is experiencing the issue?

An example of this can be found at https://wrseward.gitlab.io/ or can be seen here. This appears to also occur for other users who have at least one project using GitLab Pages (e.g. https://doctorj.gitlab.io/)

Describe what you were doing right before the issue occurred.

To reproduce follow these steps:

1. Create a new account: username
2. Create a new repository and activate GitLab Pages according to instructions at https://pages.gitlab.io/
3. Do not customize the url so that https://username.gitlab.io is not used.
4. Visit https://username.gitlab.io

I'm seeing the same problems, with further symptoms from https://gitlab.com/gitlab-com/support-forum/issues/527 Repository & site is https://alexsimkin.gitlab.io/ Also, it randomly returns me correct content and 404 (most of the times it 404. Or even first time (or a couple times) correct content and 404 onwards). Also, and you can see in build history - the artifacts seem to be correct.
Btw, I've been seeking for sites hosted at gilab.io and none found are working. (everyone has that ugly 404)

This is a known issue that will be fixed in the next release. Thanks for your report.

Should be/have been fixed by https://gitlab.com/gitlab-org/gitlab-pages/commit/b0ac2a7d3f7c48702120de4910cde34b7aee7bdd. Investigating.

@dblessing Thanks for the answer! That means that pages (on gitlab.com) won't work until may 22-th?

I opened https://gitlab.com/gitlab-org/gitlab-pages/issues/15 as a follow up. The issue may not actually be fixed.

Weird. But for me, the issue is fixed. And I'm not sure what is bringing troubles, but I've added custom 404.html, and after some time passed (and clicked Rebuild) site is rendered properly.
I'm going to deploy once again soon and will update comment if see any troubles.

@alexsimkin The sporadic issue was resolved and the remaining 404 issue affects default 404 pages, but maybe not custom ones.

Status changed to closed