Factory reset issues

I just completed a factory reset and now it says please unlock disc luks and has some letters and numbers. What is this?

I assume you have reinstalled PureOS 10? This is the passphrase that you have entered twice during the setup process when partitioned the drive.

Encryption

Disc uses LUKS encryption to ensure that the contents of the drive can’t be read in the event you loosing the laptop and some one takes the hard drive out and connected it to another machine.

It is also different to your user account. Every one will need to decrypt the hard drive before logging in.