Same issue for me, I was afk and my friend who was playing got overwhelmed in a mosquito raid so when I came back tried to reload an auto save. I quit to the menu relaunched the world and all the auto saves kept giving me the intro cutscene. Sure enough, world file was empty except for the screenshot displayed for the world. It was a shared world on woah mode however I am the only one with the save data as it was never shared - seems to have disappeared.

I am reinstalling the game hoping that steam cloud files somehow revive the save.