I did have a quick look. The side_rss block is used with our feed on the Admin Zone home page. The block will not cache if RSS failed to download (which I tested). When I tested I got "Could not open the RSS/Atom stream, https://compo.sr/backend.php?mode=news&type=rss&select=1-10&days=100 []", but that was due to me pulling out the ethernet cord rather than specifically it failing to connect to compo.sr.
It seems to happen every load but maybe I have caching turned off (will check that now). I thought it connected to Compo.sr directly but if the issue is at my end I will investigate further as to why it possibly cannot connect. I can't recall that RSS panel ever not loading so I thought it was odd.
See #4706, which resolves the missing news problem. Very complex issue, so I advise just applying patch, clearing caches, and not trying to understand it.
https://compo.sr/tracker/view.php?id=4700