Arch Linux

If I remove the directory ~/.config that solves the problem but is only temporary because if I reboot the system the problem arises again.

Try removing .local/share/kactivitymanagerd/

I removed ~/.local/share/kactivitymanagerd/.
Then I ran "/usr/bin/kactivitymanagerd start-daemon" and I get this:

org.kde.kactivities.activities: Starting the KDE Activity Manager daemon QDateTime("2015-07-09 13:19:00.860 WEST Qt::LocalTime")
kf5.kservice.sycoca: Trying to open ksycoca from "/home/kaparicano/.cache/ksycoca5"
org.kde.kactivities.application: [ OK ] loaded: "Monitor de Eventos"
Setting the name: "org.kde.ActivityManager.ActivityTemplates"
org.kde.kactivities.application: [ OK ] loaded: "Modelos de Actividades"
Setting the name: "org.kde.ActivityManager.Resources.Scoring"
Creating directory: "/home/kaparicano/.local/share/kactivitymanagerd/resources/"
KActivities: Database connection: "kactivities_db_resources_140161864534016_readwrite"
query_only: QVariant(qlonglong, 0)
journal_mode: QVariant(QString, "wal")
wal_autocheckpoint: QVariant(qlonglong, 100)
synchronous: QVariant(qlonglong, 1)
org.kde.kactivities.application: [ OK ] loaded: "Fontes do SQLite"
org.kde.kactivities.application: [ OK ] loaded: "Share-Like-Connect"
QWidget: Cannot create a QWidget without QApplication
Aborted (core dumped)

I found out If I replace compiz for kwin I am able to use power management, e.g, lock screen feature. Maybe kde5 broke friendship with compiz because in kde4 they coexisted nicely.

Please run kactivitymanagerd in gdb to get a backtrace and report it upstream

I've never used gdb. So, I did this:

$ gdb
(gdb) /usr/bin/kactivitymanagerd
Undefined command: "". Try "help".
(gdb) run
Starting program: /usr/bin/kactivitymanagerd
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
Service started, version: 6.2.0
[Inferior 1 (process 1769) exited normally]
(gdb)

You need to do

$ gdb kactivitymanagerd

and then

(gdb) run start-daemon

Once it crashes, type

(gdb) bt

to get the backtrace

Here it is:

gdb kactivitymanagerd
GNU gdb (GDB) 7.9.1
Copyright (C) 2015 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-unknown-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from kactivitymanagerd...(no debugging symbols found)...done.
(gdb) run start-daemon
Starting program: /usr/bin/kactivitymanagerd start-daemon
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
org.kde.kactivities.activities: Starting the KDE Activity Manager daemon QDateTime("2015-07-09 18:45:44.145 WEST Qt::LocalTime")
kf5.kservice.sycoca: Trying to open ksycoca from "/home/joseribeiro/.cache/ksycoca5"
org.kde.kactivities.application: [ OK ] loaded: "Monitor de Eventos"
Setting the name: "org.kde.ActivityManager.ActivityTemplates"
org.kde.kactivities.application: [ OK ] loaded: "Modelos de Actividades"
org.kde.kactivities.application: [ OK ] loaded: "Share-Like-Connect"
Setting the name: "org.kde.ActivityManager.Resources.Scoring"
Creating directory: "/home/joseribeiro/.local/share/kactivitymanagerd/resources/"
KActivities: Database connection: "kactivities_db_resources_140737353201664_readwrite"
query_only: QVariant(qlonglong, 0)
journal_mode: QVariant(QString, "wal")
wal_autocheckpoint: QVariant(qlonglong, 100)
synchronous: QVariant(qlonglong, 1)
org.kde.kactivities.application: [ OK ] loaded: "Fontes do SQLite"
org.kde.kactivities.application: Returning a valid module object for: "resources"
QWidget: Cannot create a QWidget without QApplication
[New Thread 0x7fffdd7ce700 (LWP 1891)]
[New Thread 0x7fffddfcf700 (LWP 1890)]
[New Thread 0x7fffde7d0700 (LWP 1889)]
[New Thread 0x7fffea039700 (LWP 1888)]

Program received signal SIGABRT, Aborted.
0x00007ffff5867528 in raise () from /usr/lib/libc.so.6
(gdb) bt
#0 0x00007ffff5867528 in raise () from /usr/lib/libc.so.6
#1 0x00007ffff586893a in abort () from /usr/lib/libc.so.6
#2 0x00007ffff5fe58f8 in QMessageLogger::fatal(char const*, ...) const () from /usr/lib/libQt5Core.so.5
#3 0x00007ffff5153511 in QWidgetPrivate::init(QWidget*, QFlags<Qt::WindowType>) () from /usr/lib/libQt5Widgets.so.5
#4 0x00007ffff5166453 in QDesktopWidget::QDesktopWidget() () from /usr/lib/libQt5Widgets.so.5
#5 0x00007ffff510bb3c in QApplication::desktop() () from /usr/lib/libQt5Widgets.so.5
#6 0x00007ffff7932462 in ?? () from /usr/lib/libKF5WindowSystem.so.5
#7 0x00007ffff7940d32 in NETRootInfo::currentDesktop(bool) const () from /usr/lib/libKF5WindowSystem.so.5
#8 0x00007ffff793069a in ?? () from /usr/lib/libKF5WindowSystem.so.5
#9 0x00007ffff61d418f in QAbstractEventDispatcher::filterNativeEvent(QByteArray const&, void*, long*) () from /usr/lib/libQt5Core.so.5
#10 0x00007fffebb6498e in ?? () from /usr/lib/qt/plugins/platforms/libqxcb.so
#11 0x00007fffebb659e3 in ?? () from /usr/lib/qt/plugins/platforms/libqxcb.so
#12 0x00007ffff6208ae1 in QObject::event(QEvent*) () from /usr/lib/libQt5Core.so.5
#13 0x00007ffff61d7449 in QCoreApplication::notify(QObject*, QEvent*) () from /usr/lib/libQt5Core.so.5
#14 0x00007ffff61d757b in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/libQt5Core.so.5
#15 0x00007ffff61d96b7 in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib/libQt5Core.so.5
#16 0x00007ffff622e8f3 in ?? () from /usr/lib/libQt5Core.so.5
#17 0x00007ffff205e9fd in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#18 0x00007ffff205ece0 in ?? () from /usr/lib/libglib-2.0.so.0
#19 0x00007ffff205ed8c in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#20 0x00007ffff622ecff in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#21 0x00007ffff61d4ffa in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#22 0x00007ffff61dca4c in QCoreApplication::exec() () from /usr/lib/libQt5Core.so.5
#23 0x0000000000412854 in main ()
(gdb)

Thank you for the tip arojas!

What's the status with Plasma 5.4? Did you report this upstream?

I have just checked with Plasma 5.4, and eveything is alright. Thank you very much!