Bug 465001

SUMMARY
I installed KDE Neon Testing (Plasma 5.26.90) to my Nvidia equipped Lenovo Laptop.  I have two external monitors attached, one HDMI and one Display Port.  Once I had the NVidia drivers installed and Nouveau drivers black listed, I tried to set up the two external monitors.  Using the "Display Configuration" dialog, I dragged the screens around to arrange them, made sure they were enabled and adjusted the priorities.  I applied the changes, but the monitor connected to the display port would not update.  I forget what was on the screen, either a mirror of the main screen or blank. I put the computer to sleep, and then woke it.  When it woke, the monitor connected to the display port worked as expected.

This will happen when rebooting the computer as well.  The computer will boot up, and the laptop display as well as the HDMI display work as expected.  The Display Port monitor will show a black screen with a white  logo  ( the same logo used in the tray for the Application Launcher).  The Display Port monitor can not be used until after a sleep / wake cycle.

STEPS TO REPRODUCE
1. Fresh install of KDE Neon Testing.  I started with a blank disk, no user data or settings.  On my system I had to manually install the NVida drivers with apt, and disable the Nouveau drivers, as well as disable apparmor.

2. Open Display Configuration and set up displays.  While I could set them up, Pressing "Identify" did not show anything on the Display Port connected monitor at this stage.  Apply the settings.

OBSERVED RESULT
The display port connected monitor would not display any updated image, nor was the mouse pointer rendered.  However, Plasma would allow me to for example, partially drag a window off of one screen and into the area of the non working monitor.  It wouldn't render, but Plasma thought it was okay to move a window into that area.  Same with the mouse pointer.  Instead of being stuck at the edge of the working screen, I could move it into the area of the non working screen.  I wouldn't see it, but Plasma let me move the mouse into the area.

Put the computer to sleep, and wake it up.  All worked as expected.  All three displays worked, and no matter how many times I went through seep / wake cycles, it continued to work.  However, if I reboot the computer, the Display Port monitor will not be usable until I put the computer to sleep and wake it again.


EXPECTED RESULT
All three monitors should behave normally after setting them up with the Display Configuration dialog.  Using "Identify" from that dialog should put the identification banner on each of the monitors, not just the laptop and HDMI monitors.  I should not have to put the computer to sleep and then wake it to have normal use of all three displays either when installing for the first time or when rebooting the system.

SOFTWARE/OS VERSIONS
Operating System: KDE neon Testing Edition (Updated Jan 28, 2023)
KDE Plasma Version: 5.26.90
KDE Frameworks Version: 5.103.0
Qt Version: 5.15.8
Kernel Version: 5.15.0-58-generic (64-bit)
Graphics Platform: X11
Processors: 16 × 11th Gen Intel® Core™ i7-11800H @ 2.30GHz
Memory: 15.4 GiB of RAM
Graphics Processor: Mesa Intel® UHD Graphics
Manufacturer: LENOVO
Product Name: 82JF
System Version: Legion 5 Pro 16ITH6

NVIDIA Driver Version: 525.78.01
NVML Version 12.525.78.01

ADDITIONAL INFORMATION
Originally reported as part of bug https://bugs.kde.org/show_bug.cgi?id=460341 but this is different.  Instead of multi monitor configuration being lost with every sleep / wake, now, once it is working, it stays working until I reboot.