Install from Debian apt repo -- Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)

I'm not sure whether this is the correct repository to file this issue, but this relates to installing graylog-server from the Debian sources. After setting up the apt repository according to the documentation, I'm encountering a problem when the repository is updated.

After doing a apt-get update on Debian 9, I get the following:

Get:15 http://packages.graylog2.org/debian stable InRelease [1,926 B]
Err:15 http://packages.graylog2.org/debian stable InRelease
  Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)

I notice that requests made to the packages endpoint always seem to result in a 200 result, regardless of whether the file exists. E.g, for InRelease (which doesn't exist):

$ wget --server-response -qO- https://packages.graylog2.org/debian/dists/stable/InRelease
  HTTP/1.1 200 OK
  Server: Cowboy
  Connection: keep-alive
  Date: Tue, 29 May 2018 00:10:23 GMT
  Content-Type: text/html
  Vary: Accept-Encoding
  Content-Length: 2164
  Via: 1.1 vegur

For Release:

$ wget --server-response -qO- https://packages.graylog2.org/debian/dists/stable/Release
  HTTP/1.1 200 OK
  Server: Cowboy
  Connection: keep-alive
  Date: Tue, 29 May 2018 00:10:23 GMT
  Content-Type: text/html
  Vary: Accept-Encoding
  Content-Length: 2164
  Via: 1.1 vegur

The body of the request is HTML with the Graylog header with an empty list of results.

I'm wondering whether these requests are not redirecting as they should? For e.g, should InRelease redirect (302) to Release, which in turn redirects to the file on S3? Making the request in the browser by following the hyperlinks works this way.

Graylog2 / fpm-recipes

Install from Debian apt repo -- Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?) #83