Check your network settings on the PS5 (especially the DNS settings). Maybe you use IPv6 which is not properly configured? I have that problem sometimes on my PC under Linux.
The developers are aware of this issue and are looking into it, keep upto date on everything Chivalry 2 Discord: https://discord.gg/chivalry2
I was able to finally get it to unlock. The only thing I changed from all my previous attempts is I disabled cross-play, not sure if that was it or not.