I am playing Ultimate Reloaded with some friends. Today the server crashed during start, but there was nothing special in the log. So I downloaded the map and made a reinstall. This did not work. So I decided to start the map local. I noticed that I am in the Nether. When I uploaded the map where I am not in the nether it did work again.
Now everything is fine, but I report this because other poeple may have the same problem.