I have not. Even after months, I have not found a solution. I think I found it related to the AvorionServer.exe or where the single and multiplayer "servers" launch from as they don't appear anywhere, even in the task manager as a process. I am attempting to work through it today, with the same results. I was hoping the newest updates might have patched this issue, but it has not.
Nothing has changed since then hardware wise, still running a GTX 2080TI and an Intel i7-10700K with Windows 10 Pro 21H1, and 64gb RAM.
So far, I have tested killing anti-virus, firewall, and any other programs I believed would be causing interference with the local connection, but nothing appears to be working. This even interferes with multiplayer connections still. I also do not receive any errors in my event logs that would indicate major fault. The only thing is a warming about a DistributedCOM not having Local Authority. According to Microsoft that shouldn't be killing issue, and advised against making adjustments to it for privileges.
I may have found a software conflict or issue. I run ASUS GameFirst IV as it is suppose to priorities applications' network data. I didn't think it would cause a conflict, but it appears to causing a routing issue. I kill the software and Avorion runs single and multiplayer servers multiple times with little to not issues. I am guessing in single player, GameFirst can't understand why it would route to yourself. The original problem I think started with my anti-virus, Bitdefender, seeing some programs as virus. I set the entire steam folders to be excluded to avoid future issues. I will update after some time to see if that was the resolves the issue.