The recent (18July2018) update to Minecraft 1.13 has broken the Survival Server map. There are no immediate plans to update the map generating software (overviewer), as apparently Mojang’s new chunk format is poorly documented and overviewer will require major refactoring to work with the new format.
If a compatible update becomes available, I’ll get it running as soon as possible.
The discussion about the possibility of an update is here, along with information for those who might wish to contribute money or code:
https://github.com/overviewer/Minecraft-Overviewer/issues/1454