forgot to attach guix version...
guix (GNU Guix) 13eb556f9f2b36aa729e63892a28b03b5235bf7b
clipit lacks a --version argument so I'm not entirely sure how to find its version, but I updated yesterday.
I also get this warning but I've seen it for other programs and I don't think it matters:
(clipit:2542): Gtk-WARNING **: 17:37:31.273: Unable to locate theme engine in module_path: "murrine",