When enabling third party anti-virus signature providers you must not have any other signature download scripts installed on the server otherwise it might cause problems and your server might get banned by the signature provider for excessive downloads. To fix the error uninstall the clamav-unofficial-sigs packages:
Centos/AlmaLinux/RHEL/CloudLinux
yum remove clamav-unofficial-sigs
Debian/Ubuntu
/usr/local/bin/clamav-unofficial-sigs.sh --remove-script
rm /usr/local/bin/clamav-unofficial-sigs.sh