I have this problem on multiple, very different systems.
Running: System Settings>Power>"Sleep when inactive after:" Changing from default of "Never" to any value, backing out, restarting logging in and letting system idle doesn't result in a sleep event.
I can manually put the system to sleep and wake it up just fine.
I see in /etc/systemd/logind.conf
#IdleAction=ignore
#IdleActionSec=30min
#IdleAction=ignore
#IdleActionSec=30min
As the default, regardless of what I set in the power control panel.
Otherwise on battery the systems in question will sleep on their own with an idle time set in the system's built in power control panel.
Is this a bug, are others having this issue??