RSS Feed

It looks absolutely fine when reading it through feed.ly

What did it used to look like? A feed is just an XML file, so you wont see much more than you currently do

I’m looking at it via https://katiejanecollins.com/feed/ and all it shows is ‘This XML file does not appear to have any style information associated with it. The document tree is shown below.’ followed by a load of coded text

Yep, that is the output that an RSS reader needs in order to display. If you look here:
https://feedly.com/i/spotlight/https://katiejanecollins.com/

You can see the feed looks fine.

What you are looking at is the code that Readers need in order to display your content

Hopefully that makes sense

Oh right so my feed is fine? Which means it’s definitely the images I need to sort. One has randomly appeared on my Bloglovin site, but it is the same size as all the others!? https://www.bloglovin.com/blog/13057449/followers

The feed is fine yep. What you probably need to do for them to show properly is sort the image sizes (as talked about in your other support) and then see if Blogloving likes them.