I have the same problem with Ubuntu Mate 18.04 LTS. I have enabled the guest account by creating a file /etc/lightdm/lightdm.conf with the content:
[SeatDefaults]
allow-guests=true
If I switch from the guest account to my normal account and then try to switch back to the guest account, I am locked out of the guest account. It asks for guest account password.
I have the same problem with Ubuntu Mate 18.04 LTS. I have enabled the guest account by creating a file /etc/lightdm/ lightdm. conf with the content:
[SeatDefaults]
allow-guests=true
If I switch from the guest account to my normal account and then try to switch back to the guest account, I am locked out of the guest account. It asks for guest account password.