I’ve seen this happen when there are still some A19 files in amongst A20 files. I would recommend a cleaning of files then uninstall/reinstall to be sure you only have A20 files. Bring up the game launcher and select Tools tab. Check every box then hit clean. Uninstall the game. If you have used mods in the past, go to the 7 Days folder and delete the Mods folder. Now reinstall the game. Once it’s installed, run the Verify Game File Integrity at least twice to be sure that no files were corrupted during install. At this point you should be able to generate good maps. If you have any questions on how to do any of these steps, let me know.