Check firewall rules
Run
# iptables -L -n
# iptables -L -n -t nat
Look for:
Blocked or restricted UDP traffic
Forwarding rules set to DROP
Allow forwarding
sudo iptables -P FORWARD ACCEPT
Test without firewall (temporary)
To confirm if the firewall is the issue:
sudo iptables -F
sudo iptables -t nat -F
After testing
Restart your node
Run a connection test
If it works, configure proper firewall rules instead of leaving it disabled