Me and my friends were having the same issue. We can connect just fine initially and play for multiple hours just fine. Suddenly, something will inevitably happen that will cause our host to crash. After the crash, no one can seem to reconnect, and the host can see lifeless players in the place the friends all were at the time of crash. We have tried killing those lifeless ghosts, and it did allow one reconnect, but trying it after the second crash did not work.
I understand it is early access and the multiplayer is a bit janky, but I would gladly take the crashes and having to back up to an autosave, if only we could all reconnect and play again without having to create a new map and start over.