Ok, we have several sites using K2 and RSS Feed Reader.
I have a case where one site, if updated to the latest version of K2, no longer works with RSS Feed Reader. 
This site has the latest version of Joomla and RSS Feed Reader, I have set up reading feeds from two different sites with the latest version of K2. 
www.uab.edu/rsstest/

The sources:

www.uab.edu/k2test

www.uab.edu/k2test2

Both have latest version of Joomla 3.9.25 & K2 2.10.3 
Both feeds have been checked as valid from validator.w3.org/ and have results, not empty feed.

www.uab.edu/k2test/component/k2/itemlist/tag/psychology?format=feed&limitstart=&type=rss

www.uab.edu/k2test2/component/k2/itemlist/tag/athletics?format=feed&limitstart=&type=rss  

The second feed, from k2test2 does not show, this is the site when updated to K2 no longer works. 
Any feed created off this site breaks.

 Following off this ticket with developer: www.joomlaworks.net/forum/simple-rss-feed-reader/57572-warning-failed-loading-xml?start=10  

I have checked and the "FTP layer" is not enabled on either site in the Global Configuration settings.

Testing if the allow_url_fopen is disabled on our hosting account, using the code provided:

<?phpif (ini_get('allow_url_fopen')) {echo 'allow_url_fopen is enabled';} else {echo 'allow_url_fopen is disabled';}

All sites show allow_url_fopen is enabled 

Next step, contacted our server provider:

Look in .htaccess, php.ini or .user.ini files for anything that could affect remote connecting for your site, e.g. socket_set_timeout or stream_set_timeout.If that is set to 0, you need to change it to the default of 90 seconds.

Response from provider:

The default timeout for socket based streams in php 7.2 is 60 seconds and that is its current setting. This is however defined by the setting 'default_socket_timeout'. Both 'socket_set_timeout' and 'stream_set_timeout' appear to be functions that can be called in code but are not php.ini settings. If you want us to adjust the default to 90 let me know.


Is this something I need to ask our server provider to change, will it make a difference?
Thanks,
Heather 

This is part of our problem, uab.edu/k2test2 is a clone of our news site, uab.edu/news.

The difference is k2test2 has the most current version of K2 on it and /news still has the 2.9 series of k2.
When we update the news site our feeds break.

These are the same site, cloned a few weeks ago so content will have been added but this feed should work.
Except k2test2 is update to 2.10 series of k2 and news is not.

www.uab.edu/k2test2/component/k2/itemlist/tag/academics?format=feed&limitstart=&type=rss
www.uab.edu/news/component/k2/itemlist/tag/academics?format=feed&limitstart=&type=rss
 

I'm sorry, you can't reach www.uab.edu/k2test2/ ?

We've tested the link with all the major browsers and have no issues, it's a public-facing site.

What browser are you using that is redirects to uab.edu/home instead?

Thank you for looking into this, the issue was a plugin called Phoca.
Once we removed that, everything works.
We will replace using it with a similar extension, Tagz which doesn't cause issues with the feeds.

Thank you.