Iptables-restore does not work with SNAT
Could it be related to the iptable_nat and nf_nat_ipv4 Kernel modules not being loaded as described here?
As the poster on that forum states:
“Maybe you don’t load required kernel modules? It can be, I’m guessing,
iptable_natandnf_nat_ipv4. This can be caused that you upgraded kernel package but didn't upgraded kernel modules package.”
If that all seems weird to you, sometimes if you have run a package update in an OS like Raspbian, you need to reboot the system for the new kernel modules.