The output ports seems to be non-7075, maybe try using sport 7075 instead?
Thank you for your answer.
I have done:
/sbin/iptables -t filter -A OUTPUT -p udp --dport 7075 -j ACCEPT
/sbin/iptables -t filter -A INPUT -p udp --dport 7075 -j ACCEPT
/sbin/iptables -t filter -A OUTPUT -p tcp --dport 7075 -j ACCEPT
/sbin/iptables -t filter -A INPUT -p tcp --dport 7075 -j ACCEPT
/sbin/iptables -t filter -A OUTPUT -p udp --sport 7075 -j ACCEPT
/sbin/iptables -t filter -A INPUT -p udp --sport 7075 -j ACCEPT
/sbin/iptables -t filter -A OUTPUT -p tcp --sport 7075 -j ACCEPT
/sbin/iptables -t filter -A INPUT -p tcp --sport 7075 -j ACCEPT
But it is the same


That sucks. Last option would be to check your ip6tables for rules and to also tcpdump the packets to see where they're goin.
Good idea ip6tables ! but does not work either. :-(
Fun that nobody seems running a node on Ubuntu with a firewall

I have the feeling (but not enough skills to solve) it due to the way the ports are handled with UDP (it reminds me the trouble you may have will firewall and ftp).
/sbin/iptables -t filter -A OUTPUT -p udp --dport 7075 -j ACCEPT
/sbin/iptables -t filter -A INPUT -p udp --dport 7075 -j ACCEPT
/sbin/iptables -t filter -A OUTPUT -p tcp --dport 7075 -j ACCEPT
/sbin/iptables -t filter -A INPUT -p tcp --dport 7075 -j ACCEPT
/sbin/iptables -t filter -A OUTPUT -p udp --sport 7075 -j ACCEPT
/sbin/iptables -t filter -A INPUT -p udp --sport 7075 -j ACCEPT
/sbin/iptables -t filter -A OUTPUT -p tcp --sport 7075 -j ACCEPT
/sbin/iptables -t filter -A INPUT -p tcp --sport 7075 -j ACCEPT
/sbin/ip6tables -t filter -A OUTPUT -p udp --dport 7075 -j ACCEPT
/sbin/ip6tables -t filter -A INPUT -p udp --dport 7075 -j ACCEPT
/sbin/ip6tables -t filter -A OUTPUT -p tcp --dport 7075 -j ACCEPT
/sbin/ip6tables -t filter -A INPUT -p tcp --dport 7075 -j ACCEPT
/sbin/ip6tables -t filter -A OUTPUT -p udp --sport 7075 -j ACCEPT
/sbin/ip6tables -t filter -A INPUT -p udp --sport 7075 -j ACCEPT
/sbin/ip6tables -t filter -A OUTPUT -p tcp --sport 7075 -j ACCEPT
/sbin/ip6tables -t filter -A INPUT -p tcp --sport 7075 -j ACCEPT
Does not solve the problem