Dual Identical External Monitors Fail at Same Resolution on Wayland

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Environment:

  • Distribution: Fedora 43 KDE Spin

  • KDE Plasma Version: 6.4.5 (also tested 6.5.4)

  • KDE Frameworks Version: 6.21.0

  • Qt Version: 6.10.1

  • Kernel Version: 6.17.12-300.fc43.x86_64

  • Graphics Platform: Wayland

  • Graphics Hardware: Intel Raptor Lake-S UHD Graphics (primary) + NVIDIA RTX 2000 Ada

  • Active Driver: Mesa Intel(R) Graphics

Hardware Setup:

  • Laptop: Lenovo ThinkPad P16 Gen 2 with 3840x2400 internal display (scaled 1.9x)

  • External Monitors: 2x Dell identical monitors (DEL 41176), native 1920x1080@60Hz

  • Dock: Lenovo ThinkPad Thunderbolt 3 Dock Gen 3

  • Connections: One via Thunderbolt dock DisplayPort, one via native laptop HDMI, same results when both are connected via display port to dock.

Bug Description:

Two identical external monitors fail to initialize when configured to the same resolution on KDE Wayland. The failure appears to be a race condition in the display initialization code.

Reproducible Behavior:

Both at 1920x1080 Both fail (no signal) 100% of time

Both at 1600x900 Both fail 100% of time

Mixed (1920 + 1600) intermittent disconnects every couple of seconds

One disabled Other works at any resolution100% success

Steps to Reproduce:

Connect two identical external monitors (same EDID)
Configure both to 1920x1080@60Hz via System Settings → Display Configuration
Apply settings
Observe: Both monitors report “No signal detected”

Additional Scaling Bug Observed:
There’s also a fractional scaling inheritance bug:

$ kscreen-doctor --outputs DP-2: scale: 1.0, mode: 1920x1080@60Hz

$ xrandr --query DP-2: 3648x2052 (1920x1080 × 1.9)

External monitors incorrectly inherit the laptop’s 1.9x scale factor despite KScreen showing scale=1.0. When laptop is set to scale=1.0, xrandr shows correct 1920x1080 for external monitors, but the dual-display failure persists.

Configuration Files:

~/.config/kwinoutputconfig.json shows correct configuration:

"connectorName": "DP-2",
"scale": 1,
"mode": { "height": 1080, "width": 1920, "refreshRate": 60000 }

When Did This Start:

Issue began after system updates around December 21, 2025. Previously worked correctly with identical setup.

Troubleshooting Performed:

  • Rolled back Qt 6.10.1-3 → 6.10.1-2

  • Downgraded Plasma 6.5.4 → 6.4.5

  • Downgraded Intel media drivers

  • Reinstalled NVIDIA drivers

  • Deleted all KScreen/KWin display configs

  • Tested multiple kernel versions

  • Manually set configurations via kscreen-doctor CLI

Expected Behavior:

Both external monitors should work reliably at native 1920x1080@60Hz without:

  1. Inheriting laptop fractional scaling

  2. Race conditions during initialization

  3. Requiring mixed resolutions as workaround

Logs Available:

  • No errors in dmesg during failure

  • No KWin crashes in journalctl

  • DDC communication logs show normal behavior

  • Can provide full logs if needed

Has anyone else experienced similar issues with identical external monitors on Wayland? This appears to be a regression introduced in recent KDE/Qt updates.