"Error retrieving icon"

Recently, I'd been getting a lot of rather unhelpful warnings like this in an Emacs Warnings buffer:

Warning (emacs): Error retrieving icon format-list-checks, falling back on short-text

whenever the corfu-mode completion popup thing appeared, seemingly due to kind-icon having troubles loading the SVG files for the little completion-type (aka 'kind') icons (setup like this). Googling it found a lot of AngularJS errors and only one Emacs-related one here, though that did seem to be pretty clearly a network issue. I was using the MacOS emacs-plus fork so spent a while fiddling around thinking it was due to it's allegedly poorer SVG support, but in the end I just deleted all the files in the directory svg-lib-icons-dir was set to, and voila, it now works fine. The contents of the dir had looked OK - a bunch of few-hundred byte SVG files, but after deleting them, they have not been re-created. So...I dunno.