Site Title showing broken image icon

I’ve seen this issue come up once before, but no solution was offered.

My site title comes up with a broken image icon next to it. It is bewildering me, because there are no images in the site title, just text! If delete the title completely from the ‘site identity’ tab, the broken image icon disappears. However, if I type something in – whatever it is I type – a little broken image icon suddenly pops up next to the text. It’s weird and annoying and looks rubbish. Any ideas? I’m utterly bewildered tbh!

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