As somebody mentioned about that before, I found the same problem on Debian testing installation. I have two Sparky installation of my machine; I reinstalled first one and I couldn't log in to the second one. To make sure it is not Sparky issue only, I reinstalled the first system using Debian testing installation media. The issue is the same so it came from Debian. For the installation I used the same (for system 1 and 2) SWAP partition. The installer used existing SWAP and formatted it so it gave a new UUID for SWAP. After that it's not possible to boot the second Sparky/Debian testing installation, because th SWAP UUID has been changed. To make sure it's exactly what I said, I chrooted to the second system, edited fstab and I changed the SWAP entry from UUID to dev number. After that I logged on to the second system with no problem.