External monitor goes black after login screen

External screen works fine at SDDM login and tty but right after login it goes “no signal”. It was working fine for a few hours. In “Display configuration” I constantly see “A new output has been added. Settings have been reloaded” repeatedly, without the external screen showing up. A notification popped up when coming off standby, I’m unable to login and are directed to tty2 to use “loginctl unlock-session 5”.

xrandr --listmonitors gives a strange answer:

Maximum number of clients reached
Can't open display :0

xrandr sees the ext. monitor connected:

DP1 connected (normal left inverted right x axis y axis)
   2560x1440     60.00 +  75.00  
   2560x1080     60.00    59.94  
   1920x1080     74.98    60.00    60.00    50.00    59.94  
   1920x1080i    60.00    50.00    59.94

inxi -Fazy:

System:
  Kernel: 5.15.46-1-MANJARO arch: x86_64 bits: 64 compiler: gcc v: 12.1.0
    parameters: BOOT_IMAGE=/boot/vmlinuz-5.15-x86_64
    root=UUID=50f4294d-0e3a-4d57-abe9-0dad75646905 rw quiet splash
    libata.allow_tpm=1
  Desktop: KDE Plasma v: 5 tk: Qt v: 5.15.4 wm: kwin_x11 vt: 1 dm: SDDM
    Distro: Manjaro Linux base: Arch Linux
Machine:
  Type: Laptop System: LENOVO product: 20AQ007SMS v: ThinkPad T440s
    serial: <superuser required> Chassis: type: 10 serial: <superuser required>
  Mobo: LENOVO model: 20AQ007SMS v: SDK0E50510 WIN
    serial: <superuser required> UEFI: LENOVO v: GJETA0WW (2.50 )
    date: 09/25/2018
Battery:
  ID-1: BAT0 charge: 14.7 Wh (89.6%) condition: 16.4/23.2 Wh (70.9%)
    volts: 11.9 min: 11.1 model: SANYO 45N1773 type: Li-ion serial: <filter>
    status: not charging
  ID-2: BAT1 charge: 15.4 Wh (89.5%) condition: 17.2/23.2 Wh (74.1%)
    volts: 12.0 min: 11.1 model: SANYO 45N1775 type: Li-ion serial: <filter>
    status: not charging
CPU:
  Info: model: Intel Core i7-4600U bits: 64 type: MT MCP arch: Haswell
    gen: core 4 built: 2013-15 process: Intel 22nm family: 6 model-id: 0x45 (69)
    stepping: 1 microcode: 0x26
  Topology: cpus: 1x cores: 2 tpc: 2 threads: 4 smt: enabled cache:
    L1: 128 KiB desc: d-2x32 KiB; i-2x32 KiB L2: 512 KiB desc: 2x256 KiB
    L3: 4 MiB desc: 1x4 MiB
  Speed (MHz): avg: 2052 high: 2648 min/max: 800/3300 scaling:
    driver: intel_cpufreq governor: schedutil cores: 1: 1017 2: 2648 3: 2029
    4: 2517 bogomips: 21562
  Flags: avx avx2 ht lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx
  Vulnerabilities:
  Type: itlb_multihit status: KVM: VMX disabled
  Type: l1tf
    mitigation: PTE Inversion; VMX: conditional cache flushes, SMT vulnerable
  Type: mds mitigation: Clear CPU buffers; SMT vulnerable
  Type: meltdown mitigation: PTI
  Type: spec_store_bypass
    mitigation: Speculative Store Bypass disabled via prctl and seccomp
  Type: spectre_v1
    mitigation: usercopy/swapgs barriers and __user pointer sanitization
  Type: spectre_v2 mitigation: Retpolines, IBPB: conditional, IBRS_FW,
    STIBP: conditional, RSB filling
  Type: srbds mitigation: Microcode
  Type: tsx_async_abort status: Not affected
Graphics:
  Device-1: Intel Haswell-ULT Integrated Graphics vendor: Lenovo driver: i915
    v: kernel arch: Gen7.5 process: Intel 22nm built: 2013 ports: active: eDP-1
    off: DP-1 empty: DP-2,HDMI-A-1,HDMI-A-2 bus-ID: 00:02.0 chip-ID: 8086:0a16
    class-ID: 0300
  Device-2: Chicony Integrated Camera type: USB driver: uvcvideo
    bus-ID: 2-8:6 chip-ID: 04f2:b39a class-ID: 0e02
  Display: x11 server: X.org v: 1.21.1.3 compositor: kwin_x11 driver: X:
    loaded: intel gpu: i915 display-ID: :0
  Monitor-1: DP-1 model: 27N2Q serial: <filter> built: 2021 res: 2560x1440
    dpi: 108 gamma: 1.2 size: 597x336mm (23.5x13.23") diag: 685mm (27")
    ratio: 16:9 modes: max: 2560x1440 min: 720x400
  Monitor-2: eDP-1 model: AU Optronics 0x133d built: 2013 res: 1920x1080
    dpi: 158 gamma: 1.2 size: 309x173mm (12.17x6.81") diag: 354mm (13.9")
    ratio: 16:9 modes: 1920x1080
  Message: No GL data found on this system.
Audio:
  Device-1: Intel Haswell-ULT HD Audio vendor: Lenovo driver: snd_hda_intel
    v: kernel bus-ID: 00:03.0 chip-ID: 8086:0a0c class-ID: 0403
  Device-2: Intel 8 Series HD Audio vendor: Lenovo driver: snd_hda_intel
    v: kernel bus-ID: 00:1b.0 chip-ID: 8086:9c20 class-ID: 0403
  Sound Server-1: ALSA v: k5.15.46-1-MANJARO running: yes
  Sound Server-2: sndio v: N/A running: no
  Sound Server-3: JACK v: 1.9.21 running: no
  Sound Server-4: PulseAudio v: 16.0 running: no
  Sound Server-5: PipeWire v: 0.3.52 running: yes
Network:
  Device-1: Intel Ethernet I218-LM vendor: Lenovo ThinkPad X240 driver: e1000e
    v: kernel port: 3080 bus-ID: 00:19.0 chip-ID: 8086:155a class-ID: 0200
  IF: enp0s25 state: down mac: <filter>
  Device-2: Intel Wireless 7260 driver: iwlwifi v: kernel pcie: gen: 1
    speed: 2.5 GT/s lanes: 1 bus-ID: 03:00.0 chip-ID: 8086:08b2 class-ID: 0280
  IF: wlp3s0 state: up mac: <filter>
  IF-ID-1: wwp0s20u4 state: down mac: <filter>
Bluetooth:
  Device-1: Intel Bluetooth wireless interface type: USB driver: btusb v: 0.8
    bus-ID: 2-7:5 chip-ID: 8087:07dc class-ID: e001
  Report: rfkill ID: hci0 rfk-id: 5 state: up address: see --recommends
Drives:
  Local Storage: total: 238.47 GiB used: 220.06 GiB (92.3%)
  SMART Message: Unable to run smartctl. Root privileges required.
  ID-1: /dev/sda maj-min: 8:0 vendor: Toshiba model: THNSFJ256GCSU
    size: 238.47 GiB block-size: physical: 512 B logical: 512 B speed: 6.0 Gb/s
    type: SSD serial: <filter> rev: 1102 scheme: GPT
Partition:
  ID-1: / raw-size: 238.17 GiB size: 233.38 GiB (97.99%) used: 220 GiB (94.3%)
    fs: ext4 dev: /dev/sda2 maj-min: 8:2
  ID-2: /boot/efi raw-size: 300 MiB size: 299.4 MiB (99.80%)
    used: 59.1 MiB (19.7%) fs: vfat dev: /dev/sda1 maj-min: 8:1
Swap:
  Kernel: swappiness: 60 (default) cache-pressure: 100 (default)
  ID-1: swap-1 type: file size: 8 GiB used: 0 KiB (0.0%) priority: -2
    file: /swapfile
Sensors:
  System Temperatures: cpu: 40.0 C mobo: N/A
  Fan Speeds (RPM): fan-1: 0
Info:
  Processes: 281 Uptime: 2h 39m wakeups: 4 Memory: 7.65 GiB
  used: 2.16 GiB (28.2%) Init: systemd v: 251 default: graphical
  tool: systemctl Compilers: gcc: 12.1.0 clang: 13.0.1 Packages: pacman: 1792
  lib: 474 Shell: Bash v: 5.1.16 running-in: yakuake inxi: 3.3.18

EDIT:

I could get the display to replicate the laptop screen with xrandr --auto but after restarting and attaching the external screen, plasma freezes.

Solution in my case:

In ~/.local/share/kscreen/, mv everything except just the main screen conf to .bak, including files in control and outputs.

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