Check that you don’t have Docker installed on the host, it likes to mess with networking, preventing other containers/vms from working.
If that’s not it, check that you don’t have firewalling in place on the host which would similarly prevent LXD networking from working.
If that’s still not it, check that dnsmasq is running on lxdbr0, if that’s not the case, look for conflicting DNS/DHCP server on the system.