Unable to replicate with multiple feeds including https://lorem-rss.herokuapp.com/

The issue seems to exist with the specific feed I used as an example. Using a feed created from one of my sites, the feed is displayed:

can you share a link to that feed then

Up to J4.4.0, the following feed works okay:
https://www.stadt-waechtersbach.de/service/news-feed-der-stadt-waechtersbach/rss.xml

Here the newsfeed item:

... leading to this display (with some CSS):

Here is the start of the feed:

Works fine from here

@brianteeman
So, what's wrong with my installations. The feed doesn't display under J5.0.0 on two completely different installations:

• A freshly set up J5.0.0 with no other content,
• My complex website updated to J5.0.0 (in a testdomain).

No idea as I am not sat in front of your computer. Could even be that the feed provider has blocked your ip address

@brianteeman

"Could even be that the feed provider has blocked your ip address"

No, I work closely together with them. I don't think that they would ever block an IP address.

hmm works for me too on a fresh joomla 5.0 installation same out put as brian.

Feed could not be retrieved could have several reasons, could you activate debug mode and see if you get any useful information?

@HLeithner
I can do so, but I'm not particularly good at interpreting debug mode displays. Would you like to look yourself? If yes, I can add a superuser account to both my testsites.

either way this is not a core joomla bug and should be closed here and moved elsewhere which is targetted at user support

@brianteeman
I don't completely agree. My setup has been working in numerous Joomla versions, up to and including J4.4.0. I didn't change the setup, only updated to J5.0.0. There must be a reason for that.
And I verified the issue in a fresh J5 installation.

@dautrich contact me at harald.leithner@community.joomla.org

it's likely not a joomla issue but if it works on the same server with 4.4 and not with 5.0 looks like a regression, we will see.

I checked your site and get the following out of curl for debugging:

*   Trying 80.69.201.211:443...
* Connected to www.stadt-waechtersbach.de (80.69.201.211) port 443 (#0)
* ALPN, offering http/1.1
*  CAfile: /etc/ssl/certs/ca-certificates.crt
*  CApath: /etc/ssl/certs
* SSL connection using TLSv1.3 / TLS_AES_256_GCM_SHA384
* ALPN, server accepted to use http/1.1
* Server certificate:
*  subject: CN=www.stadt-waechtersbach.de
*  start date: Dec 29 00:00:00 2022 GMT
*  expire date: Dec 29 23:59:59 2023 GMT
*  subjectAltName: host "www.stadt-waechtersbach.de" matched cert's "www.stadt-waechtersbach.de"
*  issuer: C=GB; ST=Greater Manchester; L=Salford; O=Sectigo Limited; CN=Sectigo RSA Domain Validation Secure Server CA
*  SSL certificate verify ok.
> GET /service/news-feed-der-stadt-waechtersbach/rss.xml HTTP/1.1
Host: www.stadt-waechtersbach.de
Accept: */*

* old SSL session ID is stale, removing
* Mark bundle as not supporting multiuse
< HTTP/1.1 303 See Other
< Date: Sun, 22 Oct 2023 11:02:27 GMT
< Server: Apache
< Set-Cookie: AL_SESS-S=AfdxOn42YIXV6YjZBTKK3jLuvl67Y5EFkZL6eTyPkJW3DtAymFTTOuSbj3N3dBgaJbr8; Path=/; Secure; HttpOnly; SameSite=Lax
< Content-Length: 123
< Location: /error_path/400.html?al_req_id=ZTUBQ0A6qMbMvXDVcQ7kGgAAA1M
< Content-Type: text/html
< 
* Ignoring the response-body
* Connection #0 to host www.stadt-waechtersbach.de left intact
* Issue another request to this URL: 'https://www.stadt-waechtersbach.de/error_path/400.html?al_req_id=ZTUBQ0A6qMbMvXDVcQ7kGgAAA1M'
* Found bundle for host www.stadt-waechtersbach.de: 0x7f9f8ddff7f0 [serially]
* Re-using existing connection! (#0) with host www.stadt-waechtersbach.de
* Connected to www.stadt-waechtersbach.de (80.69.201.211) port 443 (#0)
> GET /error_path/400.html?al_req_id=ZTUBQ0A6qMbMvXDVcQ7kGgAAA1M HTTP/1.1
Host: www.stadt-waechtersbach.de
Accept: */*

* Mark bundle as not supporting multiuse
< HTTP/1.1 400 Bad Request
< Date: Sun, 22 Oct 2023 11:02:27 GMT
< Server: Apache
< Cache-Control: no-cache
< Pragma: no-cache
< Connection: close
< Transfer-Encoding: chunked
< Content-Type: text/html
< 
* Closing connection 0

I'm not sure where the problem is but it looks more server like... I tried XMLReader directly, HTTPFactory (which I would expect use curl), curl directly see debug output and file_get_contents. All functions fails on this server...

Can you install me a 4.4 on the same server please and send me the login data?

@HLeithner

I don't know whether you got two e-mails that I sent to your business mail address. I've attached those mails to a response mail to this post.

The first mail gives you superuser access to my test site. The second one shows the result of checking the RSS feed with the W3C validator.

Give me some time to prepare a J4 site for you. I'll come back to you later.

I'm closing this for now, because it looks like an issue on the server (hoster or xml provider) which blocks the request. If you find out that the issues is part of joomla please feel free to reopen the issue.