As the duplicates are closed, it may be useful to note in this thread that other users have had succes by disabling the firewall of their modem/router (which would mainly be the anti DDOS functionality that you are switching off...).

Furthermore, we are especially experiencing this after I turned on the IP Flood Detection on the firewall of my modem. So before switching the firewall off entirely, switch off IP Flood Detection first to see if that helps.

We now have one person looking for a server, and after joining, have the other one look in the friends tab to join, so we don't flood it entirely.

You can still do backpack inception in .43, you just need to switch a full backpack with an empty one. Then double click the full one that is laying on the ground and it will go into the empty one on your back.