Wayland session does not start on KDE Plasma 5.21

Hello.

After a recent update to KDE Plasma 5.21, I decided to try running a wayland session.
After installing the plasma-wayland-session package, I logged into the SDDM, selected the wayland session, and logged in. After that, a black screen was displayed for a few seconds, and then the SDDM login window re-opened. In logs ~/. local/share/sddm/wayland-session.log:

wayland-session.log
No backend specified through command line argument, trying auto resolution
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5079:46: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5081:48: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5083:48: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5087:47: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5089:46: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5097:48: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5101:46: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5103:46: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5107:45: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5110:46: this compose sequence is a duplicate of another; skipping line
Compositor crashed, respawning
startplasmacompositor: Shutting down...
startplasmacompositor: Done.

If I log in to the X session and try to run command “kwin_wayland --xwayland” in the terminal, the result will be as follows:

kwin_wayland logs
No backend specified through command line argument, trying auto resolution
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5079:46: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5081:48: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5083:48: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5087:47: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5089:46: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5097:48: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5101:46: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5103:46: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5107:45: this compose sequence is a duplicate of another; skipping line
kwin_xkbcommon: XKB: /usr/share/X11/locale/en_US.UTF-8/Compose:5110:46: this compose sequence is a duplicate of another; skipping line
kf.globalaccel.kglobalacceld: Failed to register service org.kde.kglobalaccel
OpenGL vendor string:                   Intel
OpenGL renderer string:                 Mesa Intel(R) UHD Graphics 630 (CFL GT2)
OpenGL version string:                  4.6 (Core Profile) Mesa 20.3.4
OpenGL shading language version string: 4.60
Driver:                                 Intel
GPU class:                              Unknown
OpenGL version:                         4.6
GLSL version:                           4.60
Mesa version:                           20.3.4
Linux kernel version:                   5.11.1
Requires strict binding:                no
GLSL shaders:                           yes
Texture NPOT support:                   yes
Virtual Machine:                        no
kwin_core: eglPostSubBufferNV not supported, have to enable buffer preservation - which breaks v-sync and performance
Filter multi-plane format 961959257
Filter multi-plane format 825316697
Filter multi-plane format 842093913
Filter multi-plane format 909202777
Filter multi-plane format 875713881
Filter multi-plane format 961893977
Filter multi-plane format 825316953
Filter multi-plane format 842094169
Filter multi-plane format 909203033
Filter multi-plane format 875714137
Filter multi-plane format 842094158
Filter multi-plane format 909203022
kwin_core: Failed to update gamma ramp for output KWin::X11WindowedOutput(0x55e7013289d0)
_XSERVTransSocketUNIXCreateListener: ...SocketCreateListener() failed
_XSERVTransMakeAllCOTSServerListeners: server already running
kwin_core: Failed to update gamma ramp for output KWin::X11WindowedOutput(0x55e7013289d0)
The XKEYBOARD keymap compiler (xkbcomp) reports:
> Warning:          Unsupported maximum keycode 569, clipping.
>                   X11 cannot support keycodes above 255.
Errors from xkbcomp are not fatal to the X server
QObject::connect(KWin::LibInput::Connection, QObject): invalid nullptr parameter
QObject::connect(KWin::LibInput::Connection, QObject): invalid nullptr parameter

Can anyone suggest what might be the reason for this behavior?

Can you provide information about your hardware?

inxi -Fxxxza

Of cource:

Hardware details
System:    Kernel: 5.11.1-1-MANJARO x86_64 bits: 64 compiler: gcc v: 10.2.1 
           parameters: BOOT_IMAGE=/boot/vmlinuz-5.11-x86_64 root=/dev/mapper/LVM--VG-lvol--root ro 
           cryptdevice=UUID=11111111-2222-333333-444444444444:cryptroot quiet udev.log_priority=3 
           Desktop: KDE Plasma 5.21.1 tk: Qt 5.15.2 wm: kwin_x11 dm: SDDM Distro: Manjaro Linux 
Machine:   Type: Laptop System: Dell product: G5 5587 v: N/A serial: <filter> Chassis: type: 10 serial: <filter> 
           Mobo: Dell model: 0M2MWX v: A00 serial: <filter> 
Battery:   ID-1: BAT0 charge: 37.6 Wh condition: 37.6/56.0 Wh (67%) volts: 16.9/15.2 model: BYD DELL 7FHHV8A type: Li-ion 
           serial: <filter> status: Full 
CPU:       Info: 6-Core model: Intel Core i7-8750H bits: 64 type: MT MCP arch: Kaby Lake note: check family: 6 
           model-id: 9E (158) stepping: A (10) microcode: DE L2 cache: 9 MiB 
           flags: avx avx2 lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx bogomips: 52815 
           Speed: 2188 MHz min/max: 800/2200 MHz Core speeds (MHz): 1: 2188 2: 2119 3: 2200 4: 2189 5: 2196 6: 2183 7: 2200 
           8: 2200 9: 2167 10: 2200 11: 2180 12: 2196 
Graphics:  Device-1: Intel UHD Graphics 630 vendor: Dell driver: i915 v: kernel bus ID: 00:02.0 chip ID: 8086:3e9b 
           class ID: 0300 
           Device-2: NVIDIA GP106M [GeForce GTX 1060 Mobile] vendor: Dell driver: nvidia v: 460.39 
           alternate: nouveau,nvidia_drm bus ID: 01:00.0 chip ID: 10de:1c20 class ID: 0300 
           Display: x11 server: X.Org 1.20.10 compositor: kwin_x11 driver: loaded: modesetting,nvidia display ID: :0 
           screens: 1 
           Screen-1: 0 s-res: 1920x1080 s-dpi: 96 s-size: 508x285mm (20.0x11.2") s-diag: 582mm (22.9") 
           Monitor-1: eDP-1 res: 1920x1080 hz: 60 dpi: 142 size: 344x194mm (13.5x7.6") diag: 395mm (15.5") 
           OpenGL: renderer: Mesa Intel UHD Graphics 630 (CFL GT2) v: 4.6 Mesa 20.3.4 direct render: Yes 
Audio:     Device-1: Intel Cannon Lake PCH cAVS vendor: Dell driver: snd_hda_intel v: kernel 
           alternate: snd_soc_skl,snd_sof_pci bus ID: 00:1f.3 chip ID: 8086:a348 class ID: 0403 
           Device-2: NVIDIA GP106 High Definition Audio driver: snd_hda_intel v: kernel bus ID: 01:00.1 chip ID: 10de:10f1 
           class ID: 0403 
           Sound Server: ALSA v: k5.11.1-1-MANJARO 
Network:   Device-1: Intel Wireless-AC 9560 [Jefferson Peak] driver: iwlwifi v: kernel port: 5000 bus ID: 00:14.3 
           chip ID: 8086:a370 class ID: 0280 
           IF: wlp0s20f3 state: down mac: <filter> 
           Device-2: Qualcomm Atheros Killer E2400 Gigabit Ethernet vendor: Dell driver: alx v: kernel port: 3000 
           bus ID: 3c:00.0 chip ID: 1969:e0a1 class ID: 0200 
           IF: enp60s0 state: up speed: 100 Mbps duplex: full mac: <filter> 
           IF-ID-1: vpn0 state: up speed: 10 Mbps duplex: full mac: N/A 
Bluetooth: Device-1: Intel Bluetooth 9460/9560 Jefferson Peak (JfP) type: USB driver: btusb v: 0.8 bus ID: 1-14:3 
           chip ID: 8087:0aaa class ID: e001 
           Message: Required tool hciconfig not installed. Check --recommends 
Drives:    Local Storage: total: 1.16 TiB used: 218.66 GiB (18.3%) 
           SMART Message: Unable to run smartctl. Root privileges required. 
           ID-1: /dev/nvme0n1 maj-min: 259:0 vendor: A-Data model: SX8100NP size: 238.47 GiB block size: physical: 512 B 
           logical: 512 B speed: 31.6 Gb/s lanes: 4 rotation: SSD serial: <filter> rev: VB411D45 temp: 32.9 C scheme: GPT 
           ID-2: /dev/sda maj-min: 8:0 vendor: HP model: SSD S750 1TB size: 953.87 GiB block size: physical: 4096 B 
           logical: 512 B speed: 6.0 Gb/s rotation: SSD serial: <filter> rev: 4A1 scheme: MBR 
Partition: ID-1: / raw size: 184 GiB size: 180.11 GiB (97.89%) used: 40.19 GiB (22.3%) fs: ext4 dev: /dev/dm-1 maj-min: 254:1 
           mapped: LVM--VG-lvol--root 
           ID-2: /boot/efi raw size: 511 MiB size: 510 MiB (99.80%) used: 25.3 MiB (5.0%) fs: vfat dev: /dev/nvme0n1p1 
           maj-min: 259:1 
Swap:      Kernel: swappiness: 10 (default 60) cache pressure: 50 (default 100) 
           ID-1: swap-1 type: partition size: 4.47 GiB used: 0 KiB (0.0%) priority: -2 dev: /dev/dm-2 maj-min: 254:2 
           mapped: LVM--VG-lvol--swap  
Info:      Processes: 319 Uptime: 15h 53m wakeups: 3 Memory: 15.45 GiB used: 4.97 GiB (32.2%) Init: systemd v: 247 Compilers: 
           gcc: 10.2.0 Packages: 1433 pacman: 1420 lib: 425 flatpak: 13 Shell: Bash v: 5.1.0 running in: yakuake inxi: 3.3.01

On approximately the same hardware and Plasma 5.20, I was able to run a Wayland session. Then the old drives were replaced with new SSDs and the system was reinstalled. Unlike the previous installation, I now use encryption of the main partition, but I don’t think it should matter.

After upgrading to KDE Plasma 5.21.2, the problem disappeared.
I still don’t know what it might have been related to, but okay.

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