Mantic 230509 livecd requires password after auto sleep, is this a bug?

What happens when you press enter without entering a password? In the past this was the way to unlock. Also, not a bug, but the live session is not meant to be used except as a preview prior to installing.

It says unlocking failed

Sleep issues are the most common problem that I use a livecd to check.
After the multitude of failures updating to jammy from focal on every system I use (intel and amd, old and new) a preview needs to be fully functional ASAP so bugs can be filed,
Hopefully in time for the actual release.

Then sadly the empty password that the live image uses to build is actually hashed and it expects something, which may be new in Plasma or in livecd-rootfs. Either way, that's outside of the scope of the Ubuntu Studio project as it's not our bug, nor can it necessarily be considered a bug but may very well be a security feature.

A workaround is to not let it lock. As said before, the live session is not meant to be used except as a preview prior to installing or in a pinch, so if it's being used for an extended period of time, turn off the screen locker using System Settings.

Another workaround may be to use the TTY via ctrl-alt-F2 (or F3 or F4) and login using the username "ubuntustudio" and no password. Then type, "sudo systemctl restart sddm" which would restart the session.

Checking a sleep issue on a live session has a large failure rate due to the fact that many computer BIOS are set to turn off USB when suspended by default to comply with EnergyStar standards or they are hardcoded to do so. Therefore, this is a bad test and should not be tested during a live session. Additionally, the Ubuntu kernel powers-down many USB devices by default when sleeping, so this can cause a high failure rate when testing a live session. The only true test for this is to install the system in an empty partition and run the test. In other words, your test method is highly flawed.

Possibly related:

https://bugs.launchpad.net/ubuntu/+source/calamares-settings-ubuntu/+bug/198

Ubuntu Studio still asks for a password upon bootup even when autologin is selected during installation

Another workaround:
Switch to TTY &
Login as above
passwd
(Change password)
Login with the new password

I'm familiar with the bug in question (although the bug you linked is not complete and is incorrect) and it's completely unrelated.