Thanks for continuing to bring attention to this. After a detailed ticket, Obsidian sent me this e-mail in response. Issue is acknowledged I guess? I hope so... Stay tuned, I suppose. Will let you know if a resolution is found.
Hello *********,
Our team is still investigating about the multiplayer issues and looking for the best solution on this matter.
For more information or when an update is available, please stay tuned to our Grounded News page or Grounded Twitter for patch notes/notifications. We've added a Grounded Issue Tracker on our website, and a Feature Board to keep players informed on bugs and upcoming features to the game. You might also like to join our community on our forums or at our Grounded Discord.
Thanks again for reporting this issue to us and for being a fan of Grounded! Have a great rest of your day.