为什么我的系统只能在我通过 ssh 连接时进行端口转发？

Question

我使用带有内核 4.19 的 debian 10 和 nftables 作为端口转发工具。规则就像

table ip nat {
    chain prerouting {
        type nat hook prerouting priority -100; policy accept;
        ip daddr 10.250.181.103 tcp dport 25565 counter packets 0 bytes 0 log
        ip daddr 10.250.181.103 tcp dport 25568 counter packets 0 bytes 0 log
        ip daddr 10.250.181.103 tcp dport 25573 counter packets 0 bytes 0 log
        ip daddr 10.250.181.103 tcp dport 25565 counter packets 0 bytes 0 dnat to 192.168.56.1:25565
        ip daddr 10.250.181.103 tcp dport 25568 counter packets 0 bytes 0 dnat to 192.168.56.1:25568
        ip daddr 10.250.181.103 tcp dport 25573 counter packets 0 bytes 0 dnat to 192.168.56.1:25573
    }

    chain postrouting {
        type nat hook postrouting priority 100; policy accept;
        ip saddr != 192.168.56.0/24 ip daddr 192.168.56.0/24 counter packets 0 bytes 0 masquerade
    }
}

（SNAT是因为192.168.56.1是Windows，不支持策略路由）

当我 ssh 到系统时，端口转发工作正常。但是，在我注销几秒钟后它就不起作用了。

我可以检查哪些配置来找出原因？