Hi,

I've recently chosen to move from KDE Plasma 5.12(Kubuntu 18.04) to KDE Plasma 5.18 with(Kubuntu 20.04).
Turns out that it brought me a major bugg, when I disable my laptop screen and only use the external monitor connected major lagg appears. The applications are unusable, clicking a button takes a few seconds to be executed.
I eventually gave up and thought it was a Kubuntu thing, so I decided to give Manjaro 20.0.3 with KDE Plasma 5.18.5 a shot. Turns out, the same problem occurs. Just like Kubuntu, extreme lagg appears when disabling the external monitor. When both the Laptop and external monitor are on everything runs like butter.

I expect that it has something to do with the compositor. Below some screenshots:

When disabling the laptop screen I can for example make the old-school Window art:



This is what my latte-dock looks like when both my external monitor and laptop display are on.



This is what my latte-dock looks like when only my external monitor is on and the laptop display is off:



The latte-dock has a brown-ish background instead of a transparent one.

When I turn the Laptop display on again the latte-dock stays the same. When I re-apply the compositor settings it turns back to normal.

I've searched on KDE, Kubuntu and Manjaro forums and only found people with similar problems when using a DisplayLink dock. I however do NOT use a dock. The laptop and monitor are directly connected with an HDMI-cable. At this point I am stuck and using the system with both displays on which works, but is however not ideal.


System info:

HP-Pavilion 15-bc075nd
I7 6700hq with integrated Intel® HD Graphics 530
Nvidia 960m


External monitor:
LG 29UM59-P Ultrawide 2560x1080


Display settings:


Laptop Screen: Disabled
External monitor: Enabled + Primary

Compositor settings:
Scale method: Accurate
Rendering backend: OpenGL 3.1
Tearing prevention: Automatic
Keep window thumbnails: Only for shown windows