In my post KDE Komplications, I discussed some of the issues with the kactivitymanagerd program.
What kactivitymanagerd does
This program is not a system level daemon, rather it is a user space process. The kactivitymanagerd program starts when the KDE desktop is launched. It can also start when using other desktops, such as LXDE and GNOME, when a KDE application like Konqueror or Gwenview is started. I use LXDE these days due to the current level of instability in the KDE Plasma desktop.
Everything can be more or less fine until a crash occurs within a KDE application. At that point the kactivitymanagerd program is engaged and, running in user space, it creates a series of core dump files that relate to the crash of the KDE related program. This causes extremely high levels of disk activity and can have a significant negative impact on the overall performance of the affected system.
In my Internet searches I found a number of references to problems with kactivitymanagerd and various methods of dealing with it. The most successful results appear to be obtained from complete removal of this program. I used the following command to remove kactivitymanagerd.
dnf remove -y kactivitymanagerd
This command also removes some dependencies, but that is a necessary side effect of getting control of the computer back.
Here is a discussion of the issues with kactivitymanagerd.