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Linux Desktop

The cursor 'catching' at the dual-monitor boundary — an NVIDIA + Wayland bug

Environment: Kubuntu 26.04 LTS · KDE Plasma 6 · NVIDIA nvidia-driver-595-open · 2560×1440 dual monitors

TL;DR

If the cursor snags crossing between two monitors on NVIDIA proprietary + Wayland, before digging into KWin settings, test whether it reproduces in an X11 session. If it's gone under X11, that confirms an NVIDIA+Wayland issue.

# If there's no "Plasma (X11)" entry on the login screen, you need both packages
sudo apt install kwin-x11 plasma-session-x11

The symptom

With two 2560×1440 monitors side by side, moving the cursor slowly across the boundary felt like it snagged every time. It was worst when several windows were pinned to the screen edges — as if the cursor got grabbed by a resize handle, needing extra movement to break free, per what the user reported.

The misdiagnosis: "it must be catching on KWin tiling zones"

In kwinrc, each screen had KWin Quick Tiling zone settings (the translucent areas that appear when you drag a window to an edge) left as a 25%/50%/25% layout. I figured the resize handles at those zone boundaries were the snag. That was wrong.

I asked the user to actually drag a window to a screen edge, and no translucent zone overlay appeared at all — the tile editor feature was simply disabled. The settings lingering in kwinrc were just dead data. Completely the wrong tree.

Root cause: NVIDIA + Wayland multi-monitor cursor sync

The setup was nvidia-driver-595-open + a KDE Plasma 6 Wayland session. With the proprietary NVIDIA driver and Wayland, there's a known category of issue where cursor rendering doesn't sync cleanly as the cursor moves between separate monitor outputs (each with its own CRTC/pipeline).

Confirming and fixing: switch to an X11 session

I asked the user to log out and log back in via the gear icon as a "Plasma (X11)" session, then reproduce the same motion. Under X11 the symptom was completely gone. That's effectively the confirmation — it was the NVIDIA+Wayland combination, and using an X11 session is the surest fix for now.

But logging into X11 can be a problem: a default Ubuntu/Kubuntu install may not ship the X11 session at all (it didn't here — /usr/share/xsessions/ was missing entirely). Two packages are needed.

sudo apt install kwin-x11 plasma-session-x11

Installing only kwin-x11 gives you the window-manager binary; what actually makes a "Plasma (X11)" entry appear on the login screen is plasma-session-x11 (the Wayland side has its own plasma-session-wayland doing that role). It's easy to conflate the two.

Takeaways / checklist

  • For cursor/window oddities on multi-monitor, it's worth testing the Wayland vs X11 session difference before digging into KWin settings — especially with a proprietary NVIDIA driver.
  • KWin Quick Tiling zone settings (kwinrc) can linger as dead data even when the feature is off — don't assume a feature is "active now" just because a value exists; reproduce it to confirm.
  • If there's no "Plasma (X11)" login option, install plasma-session-x11 as well as kwin-x11.

Related

This X11 switch was also what confirmed the Han/Yeong key was actually sending Alt_R (that bug reproduced under X11 too), and the fake HDMI dummy plug showing up as a phantom third monitor came out of the same multi-monitor cleanup.