SUMMARY
As soon as  I boot the computer, the Activities are not working on a isolate manner. When I switch activity, the desktop wallpaper changes, but the windows follow along. For example, if I have a window opened in activity A, and I switch to activity B, the window is still presented in the other activity. 
Also, in the context menu for the window title bar (right click on title bar) the option "Show in Activities" is missing. 

As a workaround I've to log out/ log in or restart kwin. 
When that error happens, I can get the following log from joernalctl -f (the error is on the last line):

❯ journalctl -f
ago 09 10:02:15 deckro xdg-desktop-portal-kde[1284]: xdp-kde-settings: Key  "font"  doesn't exist
ago 09 10:02:15 deckro xdg-desktop-portal-kde[1284]: xdp-kde-settings: Key  "activeFont"  doesn't exist
ago 09 10:02:15 deckro xdg-desktop-portal-kde[1284]: xdp-kde-settings: Key  "toolBarFont"  doesn't exist
ago 09 10:02:15 deckro xdg-desktop-portal-kde[1284]: xdp-kde-settings: Key  "smallestReadableFont"  doesn't exist
ago 09 10:02:31 deckro plasmashell[1242]: Could not find the Plasmoid for Plasma::FrameSvgItem(0x563046d9b400) QQmlContext(0x5630471100e0) QUrl("file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/global/Globals.qml")
ago 09 10:02:31 deckro plasmashell[1242]: Could not find the Plasmoid for Plasma::FrameSvgItem(0x563046d9b400) QQmlContext(0x5630471100e0) QUrl("file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/global/Globals.qml")
ago 09 10:02:31 deckro flatpak[1567]: flameshot: info: Capture saved to clipboard.
ago 09 10:02:31 deckro systemd[1108]: app-flatpak-org.flameshot.Flameshot-2778.scope: Consumed 1.283s CPU time.
ago 09 10:02:36 deckro kwin_x11[1202]: kwin_core: XCB error: 152 (BadDamage), sequence: 40781, resource id: 16784681, major code: 143 (DAMAGE), minor code: 3 (Subtract)


It doesn't happen all the time, so I'm still unable to determine what is the probable  cause of it. 


STEPS TO REPRODUCE
1.  Cold boot the system, and login normally. 
2. Have at least two activities set up. 
3. Open any window
4. Switch activity (using activity switcher, keyboard shortcut, or any other way)


OBSERVED RESULT
The wallpaper changes (if they are setup per activity) , the activity switcher (if enabled) indicates that the activity changed, but the windows get carried along. As if  the window was set up to show in all activities. 
Also, the window title bar "Show in activities" context menu is not displayed. 

EXPECTED RESULT
The window is only displayed in it's original activity, and the windows title bar context menu "Show in activities" item is available. 

SOFTWARE/OS VERSIONS
OS: Manjaro Linux x86_64
Kernel: 6.1.41-1-MANJARO
Shell: zsh 5.9
Resolution: 2560x1440, 1920x1080
DE: Plasma 5.27.6
WM: KWin
WM Theme: Oxygen
Theme: [Plasma], Adwaita-dark [GTK2/3]
CPU: Intel i7 4790H
GPU: AMD ATI Radeon 6600
Memory: 32043MiB