This happened to me now a couple of times, "Error loading saved data: villages", new is that "raids" has been added now into the error in the game output.

All I did was to re-create a previously created (also in the snapshots, 18w50a to be precise) world and entering it.

I am certain this must have been reported already on the bugtracker, but again I just cannot find it with the search terms I used.

Thus, to be safe, reporting it, even if it may get resolved as duplicate.