Plasma taskbar disappeared spontaneously.
Everything is updated (no updates available at the moment). Rebooted many times (including on previous kernel).
The old hack (suggested from dead/crashed forum) killall plasmashell; plasmashell > /dev/null 2>&1 & disown which worked previously - does not help anymore. Neither killall plasmashell; plasmashell &.
Details:
$ inxi -Fb
System: Host: roman-pc Kernel: 5.8.6-1-MANJARO x86_64 bits: 64 Desktop: KDE Plasma 5.19.5 Distro: Manjaro Linux
Machine: Type: Laptop System: Dell product: G3 3779 v: N/A serial: <superuser/root required>
Mobo: Dell model: 04R93M v: A00 serial: <superuser/root required> UEFI: Dell v: 1.2.1 date: 07/18/2018
Battery: ID-1: BAT0 charge: 6.1 Wh condition: 24.9/56.0 Wh (44%)
CPU: Topology: 6-Core model: Intel Core i7-8750H bits: 64 type: MT MCP L2 cache: 9216 KiB
Speed: 1327 MHz min/max: 800/4100 MHz Core speeds (MHz): 1: 804 2: 818 3: 815 4: 801 5: 810 6: 845 7: 906 8: 802
9: 806 10: 802 11: 801 12: 801
Graphics: Device-1: Intel UHD Graphics 630 driver: i915 v: kernel
Device-2: NVIDIA GP106M [GeForce GTX 1060 Mobile] driver: nvidia v: 450.66
Device-3: Realtek Integrated Webcam type: USB driver: uvcvideo
Display: x11 server: X.Org 1.20.8 driver: modesetting,nvidia resolution: 1920x1080~60Hz
OpenGL: renderer: GeForce GTX 1060 with Max-Q Design/PCIe/SSE2 v: 4.6.0 NVIDIA 450.66
Audio: Device-1: Intel Cannon Lake PCH cAVS driver: snd_hda_intel
Device-2: NVIDIA GP106 High Definition Audio driver: snd_hda_intel
Sound Server: ALSA v: k5.8.6-1-MANJARO
Some related records from KSystemlog:
27.09.20 17:17 kdeinit5 Qt: Session management error: networkIdsList argument is NULL
27.09.20 17:18 plasma_waitforname org.kde.knotifications: WaitForName: Service was not registered within timeout
27.09.20 17:18 dbus-daemon [session uid=1000 pid=918] Activated service 'org.kde.KSplash' failed: Process org.kde.KSplash exited with status 1
27.09.20 17:22 kwin_x11 qt.qpa.xcb: QXcbConnection: XCB error: 3 (BadWindow), sequence: 43830, resource id: 102760456, major code: 18 (ChangeProperty), minor code: 0
27.09.20 17:25 kwin_x11 Could not attach Keys property to: PlasmaQuick::Dialog(0x559e985c0ec0) is
not an Item
27.09.20 17:25 kwin_x11 file:///usr/share/plasma/look-and-feel/org.kde.breeze.desktop/contents/
windowswitcher/WindowSwitcher.qml:62:17: QML Connections: Implicitly defined onFoo properties in
Connections are deprecated. Use this syntax instead: function onFoo(<arguments>) { ... }
27.09.20 17:25 kwin_x11 file:///usr/lib/qt/qml/QtQuick/Controls/Styles/Plasma/ScrollViewStyle.qml:60:5:
QML Connections: Implicitly defined onFoo properties in Connections are deprecated. Use this syntax
instead: function onFoo(<arguments>) { ... }
27.09.20 17:25 kwin_x11 Qt Quick Layouts: Detected recursive rearrange. Aborting after two iterations.
27.09.20 17:25 kwin_x11 file:///usr/lib/qt/qml/org/kde/plasma/components/Highlight.qml:47:5: QML
Connections: Implicitly defined onFoo properties in Connections are deprecated. Use this syntax
instead: function onFoo(<arguments>) { ... }
27.09.20 17:25 kwin_x11 qt.qpa.xcb: QXcbConnection: XCB error: 3 (BadWindow), sequence: 15639,
resource id: 14764275, major code: 3 (GetWindowAttributes), minor code: 0
27.09.20 17:25 kwin_x11 qt.qpa.xcb: QXcbConnection: XCB error: 9 (BadDrawable), sequence: 15640,
resource id: 14764275, major code: 14 (GetGeometry), minor code: 0
27.09.20 17:25 kwin_x11 qt.qpa.xcb: QXcbConnection: XCB error: 3 (BadWindow), sequence: 15643,
resource id: 14764275, major code: 3 (GetWindowAttributes), minor code: 0
27.09.20 17:25 kwin_x11 qt.qpa.xcb: QXcbConnection: XCB error: 9 (BadDrawable), sequence: 15644,
resource id: 14764275, major code: 14 (GetGeometry), minor code: 0
27.09.20 17:25 kwin_x11 Qt Quick Layouts: Detected recursive rearrange. Aborting after two iterations.
27.09.20 17:25 kwin_x11 file:///usr/lib/qt/qml/org/kde/plasma/components/Highlight.qml:47:5: QML
Connections: Implicitly defined onFoo properties in Connections are deprecated. Use this syntax
instead: function onFoo(<arguments>) { ... }