Looks like I found the upstream bug report on GitHub:
https://github.com/mate-desktop/mate-screensaver/issues/92
(Couldn't link it into this ticket though, Launchpad does not recognize it somehow...)
Also the Ubuntu MATE Community Forum has a thread on this topic, too:
https://ubuntu-mate.community/t/automatic-lock-screen-not-activating/5696/16
Looks like I found the upstream bug report on GitHub:
https:/ /github. com/mate- desktop/ mate-screensave r/issues/ 92
(Couldn't link it into this ticket though, Launchpad does not recognize it somehow...)
Also the Ubuntu MATE Community Forum has a thread on this topic, too:
https:/ /ubuntu- mate.community/ t/automatic- lock-screen- not-activating/ 5696/16