Screen not restarting after being locked for hours

[lah7]

This sounds like the issue in this topic - likely your monitor is seen as "unplugged" when it's turned off and causes a glitch in MATE Screensaver, which is responsible for presenting the lock screen.

[Security issue] Lock-screen not retained when exit screensaver with TV hdmi

On my 18.04, if I lock my session, when exit the screensaver, in particular conditions, my session is no longer locked and it is accessible without typing password. In terms of security, it’s ugly. The lock-screen works fine, because if I lock my session, the password is required before the screensaver appears. As soon as the screensaver activates, then when exit screensaver, no more lock-screen. My display is a TV plugged in HDMI that I switch off after enabled lock-screen. Sometimes, the lock-…

The bug has been fixed, but unfortunately the fix hasn't been applied to 18.04 due to SRU approval issues.

• Bug #1768352 “mate-screensaver screen lock can be bypassed by po...” : Bionic (18.04) : Bugs : mate-screensaver package : Ubuntu

Try updating the packages manually and see if this fixes your issue:

@lah7

You can still install the new mate-screensaver 1.20.2 in the meantime by using the packages built for Cosmic at https://launchpad.net/ubuntu/+source/mate-screensaver/1.20.2-1 under Builds .

The downloads are:

• mate-screensaver-common_1.20.2-1_all.deb (4.4 MiB)
• mate-screensaver_1.20.2-1_amd64.deb (128.1 KiB) (64-bit only)
• mate-screensaver_1.20.2-1_i386.deb (135.9 KiB) (32-bit only)

Then install them via the terminal:

sudo dpkg -i mate-screensaver-common_*.deb mate-screensaver_*.deb

Then restart your session or computer.