Kubuntu 26.04: Black screen after screen lock or display power off (Wayland, NVIDIA RTX 3070)

[Yamanqui]

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 appears to trigger the same behavior

Steps to reproduce

1. Log into a Plasma Wayland session.
2. Run:
   loginctl lock-session
   
   (or wait for the screen to lock/power off automatically.)
3. 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.

[die.boer]

can you check if this happens on X11 too ?
If X11 works normally,then your hardware is fine,Plasma itself is probably fine then the issue is almost certainly a Wayland/NVIDIA interaction.