I have a VPS running Debian 10 as OpenVPN server that is forwarding a public port to a different port of an OpenVPN client using ufw:

in /etc/ufw/before.rules i added

*nat
:PREROUTING ACCEPT [0:0]
-A PREROUTING -d server_ip -p tcp --dport 8200 -j DNAT --to-dest VPN_client_ip:444

:POSTROUTING ACCEPT [0:0]
-A POSTROUTING -s VPN_subnet/24 -o eth0 -j MASQUERADE
-A POSTROUTING -d VPN_client_ip -p tcp --dport 444 -j SNAT --to-source server_ip

If I flush all iptables rules using

iptables-save | awk '/^[*]/ { print $1 }
                        /^:[A-Z]  [^-]/ { print $1 " ACCEPT" ; }
                        /COMMIT/ { print $0; }' | iptables-restore

and then do

ufw reload

it works just fine. But this removed the docker iptables rules. Restarting docker readds them and breaks the forwarding. Any ideas why? How can I diagnose this problem?