The startup Dashboard stops working when you change the sudo-policy using visudo. You will have to manually invoke sudo pt-os-dashboard from terminal on every logon and type in your root password afterwards to make it show up again.
Please fix this in future upgrades.
PS: I don't like the Ubuntu approach with privilege escalation without supplying root credentials. It is insecure and potentially a threat if you for instance leave your Pi-Top logged in during a break in classroom, and somebody opens up a terminal and fires a malicious command (like
dd if=/dev/urandom of=/dev/mmcblk0 NEVER RUN THIS COMMAND WITHOUT A COMPLETE SYSTEM BACKUP!!!).
You can add the command pt-os-dashboard to you /etc/rc.local file just before the line of "exit 0", and the dashboard will work again.