I'm having the same issue in a Guix System. After a pull and reconfigure all the fonts in Xfce are messed up. After a lot of meddling and help from #guix IRC, it seems installing font-dejavu and running fc-cache -rv after that "solves" the problem. I have done the guix pull and reconfigure in multiple Guix VMs, both with "sudo -i" and normally, just in case the underlying system is out of date and causing these issues, but they all lead to the same situation.