lost+found is a system folder used by checkdisk to put inodes that are not marked as deleted but is not attached to any file inode. In effect, this is where checkdisk places file remnants that are recovered but with no file name
Therefore you are not allowed to mess with it if you are not root, and only then if you first change permissions on the folder. It is unwise to do anything with lost+found directories unless you know exactly what you are doing. Placing files there and encrypting does not sound like "know exactly what you are doing" and therefore I recommend "Hands off".