I got this weird bug that tells that the Kubuntu installer has crashed. I tried to install three times and the same thing happened. Later I changed the file format of the root partition and everything got sorted out. The problem was that I was using btrfs as the file format for the root partition, which led to the error. Now that I have changed to ext4 for root, Kubuntu installs fine. You can use btrfs for other partitions like /home and not for root at the moment.