had same issue. logged off, when trying to continue later, i needed to create a new char. This new char spawned on my first island. My house was still there and I was able to access everything. After i made a new ship and went back to where i was last, no tombstone or inventory. everything lost. There shouln't have been even any reason to create a new char, as I was safe on the roof of my house.
I don't understand why in single player the server need to safe the game, as this seems to be buggy and I do not see any reason for why it must be server sides. We should be able to maintain our own backups, so we have what we saved!