There's a temporary issue with Zero-K not displaying the download progress. This is caused by an error within the user interface of the downloader, the download is still running in the background.
Press the "Rescan Files" button under "Downloads" and rejoin your battle room after waiting a few moments for the download to finish. The map/mod should now be available to play on.This issue
has been resolved. Restart the game to get the new version.The auto update doesn't work for me though, so maybe another fix is needed.. Reinstalling should definitely work.