I’m facing the same with firewalld.
If I restart firewalld, all the iptables set by LXD are removed so I must restart LXD or the containers will be disconnected of outgoing internet connections.
I’m trying to find a way to manually set the right iptables rules LXD is setting. So that I could integrate these rules inside the firewalld parameters and set ipv4.firewall=false in the LXD parameters.
Did you find a way to do that? or do you just force LXD reload after your firewall restart?