Main RSS feed validates; category RSS feed fails with gzip issue

I am troubleshooting the RSS feeds from a website I’m working on.

The main feed for the site, https://aptpuo.jungle.ca/feed/rss/ validates correctly.

But the feed for a particular category of posts https://aptpuo.jungle.ca/category/news/feed fails with a warning that the feed is not a gzipped file even though the server has declared it to be.

If it’s truly a misconfigured server (ie mod_deflate should be doing something different) why does the regular feed work?

And if it is in fact an issue with mod_deflate, what should I do to correct it?

The page I need help with: [log in to see the link]