I found that after doing an upgrade rather than a fresh install, of Fedora 26 with XFCE, the NetworkManger applet was sometimes delay appearing and sometimes unresponsive. This is down to the notifications system not working.
If you try the notifications system, you should see a pop-up appearing with the words “Test Message” if you send this as a normal user :-
notify-send Test “Test Message”
If this does not work, you may be suffering from this issue.
It turns out that if you look in the directory /usr/share/dbus-1/services/,
you will see two dbus notifications, one for KDE and one for XFCE, and these are conflicting with each other. The fix is to remove the KDE notification and leave the XFCE notification
Leave this :-
/usr/share/dbus-1/services/org.xfce.xfce4-notifyd.Notifications.service
Remove this :-
/usr/share/dbus-1/services/org.kde.plasma.Notifications.service
Restart your session and you will find that the notifications now work, and that the NetworkManager applet is responsive.