Yes...

I glanced at the recent posts on my phone, saw your reply, so I tapped on the link there - and it came up with the correct links, as it does for you.

Back on my PC now, and the posts that have appeared since mine are stil not clickable in my RSS reader, and looking at the RSS feed itself, it still shows them without the http: and therefore unclickable.

Which is very, very odd.

And I've just copied and pasted the address bar from the open RSS feed page into a different web browser - and the links there are all correct.

So on the face of it, the problem isn't with the forum, it's something at my end - but I'm baffled as to what? The RSS reader isn't exhibiting this problem for any other feed, and it's affecting both that and the browser I normally use. Colour me baffled.

Edit: I forgot about Thunderbird's ability to read RSS feeds. That also gives me forum posts that can't be clicked on - so it's actually affecting three different programs.

Bah!

I'll (obviously) see what happens on Windows when I set up at a client later. Given that it's affecting three different programs on this Linux box (my reader, Firefox, and Thunderbird), but one other program remains unaffected (Chrome*) I'm not sure that the platform itself is the issue - that said, you and Joanne both don't see the issue on Windows, and I didn't when I checked on Android. Odd.

I don't run an RSS reader on Windows as well as Linux, because I'd end up seeing the RSS feed contents twice for most feeds I read. (It would be less of a problem for this site, though, because the RSS feed contains so few posts - I'd probably see stuff I'd otherwise miss.)

What I do instead is glance at the recent posts (or equivalent on other sites) occasionally when I have a few spare minutes - but that's a bit hit and miss (lots of sites I like to read, whether or not I decide to post anything to any of them, whether I want to spend those spare few minutes at or away from the computer, and so on.)

That said... while drifting off to sleep I pondered whether or not I can:

(a) Find an RSS reader that is available for both Windows and Linux.
(b) And whether that reader will allow me to configure where it stores its data.

There will be readers-a-plenty available for both platforms, so (a) won't be a problem (RSSOwl springs immediately to mind, for example) - but (b) will be more interesting. If I can find one that allows that, then I can move the program's raw data - the feeds it's downloaded and all its associated data, such as what has/hasn't been read - into pCloud. That way the feeds should in theory be synchronised across both platforms.

* Looking at the page source in Chrome, the links are the same as I described above - they lack https: - but Chrome is treating them as remote links and therefore showing them correctly. This suggests the problem is how the other three are handling the links in the feed, but in other feeds I have the link does come with the http: prefixed. And, as I said, up until 10th July, it was working for this site. Something changed then. (The reader itself hasn't changed, but perhaps a library or something it uses has, and it's also used by Thunderbird/Firefox?)

Yes - I've looking now in my Windows browser (Palemoon, a Firefox derivative) and it's not working here. That rules out a component on the Linux machine that affects all three programs in which I'm seeing the problem there.

"I'm guessing that spark have made a change to their forum software"

That seems the most likely explanation.

"as, certainly for the web, it's no longer necessary to include it,"

That's only true to a certain extent. Within a website, for example, it isn't necessary if using local/relative links - but linking to an external site does require the protocol; doing so helps tell the browser the link isn't a local, relative one. But also, as you note:

"without taking into account that rss feeds would be affected."

Exactly. The RSS feed is (more often than not, I should imagine) read by a separate program - so specifying local, relative links (which might sound logical, because the feed is local to the site) is a bit flawed. :/

If I have time later, I might gander their site for examples of other forums using their software (so I can glance at them and see if it affects all sites using it) and/or a contact address to point out the problem.