Hi,
Having the same issue, in ~/.xsession-errors I get the following two lines whenever I try to leftclick on a taskbar window:
file:///usr/share/plasma/plasmoids/org.kde.plasma.taskmanager/contents/ui/ContextMenu.qml:509: TypeError: Cannot read property 'LauncherUrlWithoutIcon' of undefined
file:///usr/share/plasma/plasmoids/org.kde.plasma.taskmanager/contents/ui/ContextMenu.qml:77: TypeError: Cannot read property 'LauncherUrlWithoutIcon' of undefined
D.