After KDE neon crashed because of development. It looks BTRFS file system got corrupted so that I can't enter and revert to snapshot. The error in installation is as follows: [11.426553] BTRFS error (device nvme0n1p6) qgroup generation mismatch, marked as inconsistent
The system doesn't boot from the liveDVD version neon-useredition-20170518-1018-amd64
This looks like a BTRFS issue, followed by a system issue regarding it's inability to boot from CD.