TCP connections Zombies?

Hi folks !
I would like advice from the community.
Yesterday we probably get something like a DOS attack. Our server was down and unable to reconnect by the remote connection.
From this day it seems that the server get a lot (40+) TCP connections “open”.
What seems weird for me is the pattern of these opened connections :

Imgur

What is strange: the process is “unknown” without PID , the local port is 30120, the local AND the remote address is the loopback IP and the remote port is “random” port from 50000 yesterday and today the range of these port is 56400.

What I did first is to add a timeout on TCP connection : 30s to prevent getting too much opened connections making down the server.

FYI : Windows Server 2019
AMD RYZEN 9 PRO 3900 12-Core 3.09GHZ - 128GB RAM

For the firewall rules is there some tricks to prevent unauthorized connection (if these connections are not normal)

Thank your for your feedback