I have had the same error since initial installation (24.7). Log files were getting flooded with errors so I switched to DNSMasq. Now need wildcard hostname resolution so turned Unbound back on, all default settings apart from "Register ISC DHCP4 Leases" and "Register DHCP Static Mappings". OPNSense is now on (25.1.2) but the errors are the same as when on (24.7) with unbound enabled.