NFTABLE issue: IPv6 does not behave like IPv4 with mirror config

I have an issue with IPv6 on my server. I have nginx configured to listen on port 443 from IPv4 and IPv6. And it works great: my webiste is available form Internet with TLS enabled.

Things get complicated when I activate nftables: when I am accessing my website from IPv4 it works, but when I access it from IPv6 connections time out :(

Output of sudo nft list ruleset:

table inet filter {
        chain INPUT {
                type filter hook input priority filter; policy drop;
                meta nftrace set 1
                ct state established,related accept comment "allow established connections"
                iif "lo" accept comment "allow all from localhost"
                iif != "lo" ip daddr 127.0.0.0/8 counter packets 0 bytes 0 drop comment "drop connections to loopback not coming from loopback"
                iif != "lo" ip6 daddr ::1 counter packets 0 bytes 0 drop comment "drop connections to loopback not coming from loopback"
                iifname "tunnel0" accept comment "allow all from VPN"
                udp dport 12345 accept comment "allow VPN on port 12345"
                tcp dport { 22, 80, 443 } accept comment "allow HTTP, HTTPS and SSH on classic ports"
        }

        chain OUTPUT {
                type filter hook output priority filter; policy accept;
        }

        chain FORWARD {
                type filter hook forward priority filter; policy drop;
        }
}

Output of sudo nft monitor trace | grep 443:

trace id 76d7cb1a inet filter INPUT packet: iif "eth0" ether saddr AA:AA:AA:AA:AA:AA ether daddr BB:BB:BB:BB:BB:BB ip6 saddr 2a01:cb09:804b:cd61:CCCC:CCCC:CCCC:CCCC ip6 daddr 2001:CCCC:CCCC:CCCC::CCCC ip6 dscp cs0 ip6 ecn not-ect ip6 hoplimit 45 ip6 flowlabel 0 ip6 nexthdr tcp ip6 length 40 tcp sport 53184 tcp dport 443 tcp flags == syn tcp window 22240

Note I do not have this issue with ssh on port 22. I am running nftables v0.9.8 (E.D.S.) on Debian 11.

I almost spent a day looking for the solution. Any help is welcome! Thank

This did the trick for me:

table inet filter {
    chain INPUT {
        type filter hook input priority 0; policy drop;

        meta l4proto ipv6-icmp accept
        ip6 ecn not-ect accept

        # Although I used the slightly more restrictive:
        # ip6 ecn not-ect ip6 hoplimit 1 accept
    }
}

Notice that the packet you captured is an ECN packet, just like mine (except mine has ip6 hoplimit 1 from a link-local fe80::/10 saddr, while yours has ip6 hoplimit 45). It seems this packet must be accepted in order to get assigned an IPv6 block by my ISP (Spectrum Broadband), and perhaps you're having similar difficulties related to these ECN packets.