Multiplayer seems to work but not with custom ship designs. I tried to play with a friend earlier and it didn't work no matter who hosted, each time the game would crash or time out. I know we didnt have this issue earlier in the week.
After moving all custom ship designs out of the designs folder, the multiplayer works, but only using the prefab ship designs the game creates. Not those i spent hours making. These designs still appear to work fine in single player.
So there's the work around for those trying to play multiplayer but keep crashing. Or a possible one anyway. I hope the Devs are working on fixing this so we can use our own designs in multiplayer as well. It's still fun to play without them, but we really want to play with our customs.