Hi!
Environment:
Linux Archi 4.6.1-2-ARCH #1 SMP PREEMPT Thu Jun 2 15:46:17 CEST 2016 x86_64 GNU/Linux
Qt: 5.6.0
KDE Frameworks: 5.22.0
Hardware: Dell latitude E5450
00:00.0 Host bridge: Intel Corporation Broadwell-U Host Bridge -OPI (rev 09)
00:02.0 VGA compatible controller: Intel Corporation Broadwell-U Integrated Graphics (rev 09)
00:03.0 Audio device: Intel Corporation Broadwell-U Audio Controller (rev 09)
00:04.0 Signal processing controller: Intel Corporation Broadwell-U Processor Thermal Subsystem (rev 09)
00:14.0 USB controller: Intel Corporation Wildcat Point-LP USB xHCI Controller (rev 03)
00:16.0 Communication controller: Intel Corporation Wildcat Point-LP MEI Controller #1 (rev 03)
00:19.0 Ethernet controller: Intel Corporation Ethernet Connection (3) I218-LM (rev 03)
00:1b.0 Audio device: Intel Corporation Wildcat Point-LP High Definition Audio Controller (rev 03)
00:1c.0 PCI bridge: Intel Corporation Wildcat Point-LP PCI Express Root Port #1 (rev e3)
00:1c.3 PCI bridge: Intel Corporation Wildcat Point-LP PCI Express Root Port #4 (rev e3)
00:1c.4 PCI bridge: Intel Corporation Wildcat Point-LP PCI Express Root Port #5 (rev e3)
00:1d.0 USB controller: Intel Corporation Wildcat Point-LP USB EHCI Controller (rev 03)
00:1f.0 ISA bridge: Intel Corporation Wildcat Point-LP LPC Controller (rev 03)
00:1f.2 SATA controller: Intel Corporation Wildcat Point-LP SATA Controller [AHCI Mode] (rev 03)
00:1f.3 SMBus: Intel Corporation Wildcat Point-LP SMBus Controller (rev 03)
01:00.0 SD Host controller: O2 Micro, Inc. SD/MMC Card Reader Controller (rev 01)
02:00.0 Network controller: Intel Corporation Wireless 7265 (rev 59)
03:00.0 3D controller: NVIDIA Corporation GM108M [GeForce 840M] (rev a2)

Drivers:
$pacman -Qs intel
local/lib32-mesa 11.2.2-1
an open-source implementation of the OpenGL specification (32-bit)
local/libva-intel-driver 1.7.0-1
VA-API implementation for Intel G45 and HD Graphics family
local/mesa 11.2.2-1
an open-source implementation of the OpenGL specification
local/xf86-video-intel 1:2.99.917+654+ga508b11-1 (xorg-drivers xorg)
X.org Intel i810/i830/i915/945G/G965+ video drivers
$ pacman -Qs nvidia
local/libvdpau 1.1.1-2
Nvidia VDPAU library
local/xf86-video-nouveau 1.0.12-1 (xorg-drivers xorg)
Open Source 2D acceleration driver for nVidia cards

Problem:
In my Job i need laptop and second monitor when i work stationary. I connect laptop to monitor use HDMI cable. When i create new user and first time connect monitor everythink is ok, i can set main display in setting but when i several time disconnect and connect monitor, KDE gone crazy. Symptoms:
Sometime is black screen with cursos on laptop screen after login, i cant do anythinh but when i connect monitor by hdmi everythink is work
Sometime i dont have program panel on laptop screen
Sometime kde is freeze and i cant click anywhare in both display or in one of them
Sometime kde is freeze and i must logout use alt+ctrl+backspace

My video:
https://www.youtube.com/watch?v=8g8Nx0OXSwc
https://www.youtube.com/watch?v=-R22MB4kupA

This problem has some similarities to my problem to "unify displays" http://goo.gl/ISVTaJ https://youtu.be/PUW33XSKjik

The feedback I was getting is that monitor problems would only be sorted out with Plasma 5.6 I did try Plasma 5.6 from the ppa, and it seemed to solve my unify display problem, but there were other instabilities, so I am waiting for a more stable subversion of Plasma 5.6.

Plasma 5.7.5 solved my problem https://youtu.be/Tor-zcJhJDY

Same problem with Plasma 5.15.5. When I plug to the docking station, my two additional screens turn black but if I do Ctrl+Alt+F2 I see the console on all three screens.