I upgraded from Kubuntu 25.10 to Kubuntu 26.04 LTS. Since the upgrade, my graphical session becomes unusable whenever the screen locks or the display powers off.
System
- Kubuntu 26.04 LTS
- KDE Plasma 6.6.5
- Wayland session
- Linux kernel 7.0.0-27-generic
- NVIDIA GeForce RTX 3070
- NVIDIA driver 580.159.03
Problem
The issue occurs in at least these situations:
- The screen locks (
loginctl lock-session) - The display powers off after inactivity
- Suspend also triggers the same behavior
Steps to reproduce
-
Log into a Plasma Wayland session.
-
Run:
loginctl lock-session(or wait for the screen to lock/power off automatically.)
-
Attempt to wake the session.
Expected behavior
The lock screen should appear and the session should be usable after entering the password.
Actual behavior
- The monitor wakes up to a black screen.
- The mouse cursor is visible and can be moved.
- Typing the password does not restore the session.
- Ctrl+Alt+F2 (or another TTY) still works.
- The system itself appears to remain running.
Additional observations
From a TTY, I tried:
systemctl --user restart plasma-kwin_wayland.service
This changed the display to what looked like the graphical login screen. The clock updated, the mouse worked, and I could type my password. However, pressing Enter caused the graphical interface to freeze completely.
From another TTY I then tried:
systemctl restart sddm
After this, the screen became black with only a white cursor/underscore in the upper-left corner, and even switching to another TTY no longer worked. I had to power-cycle the machine.