I’ve been using manjaro with KDE Plasma for a few years now, but this issue started recently, this week, and not even after an update, so I’m not sure what triggered it.
Currently in htop, plasmashell is sitting at 75% CPU usage and kactivitymanagerd is at 29%. So, together, they are pinning one CPU core, making the fan run and the laptop gets hot. This happens right from login time and never seems to stop (laptop has been on for hours). Rebooted multiple times, no change.
Any idea what could be causing this? I did find this recent-ish reddit thread where an Arch+Plasma user has a very similar issue. They suggested changing the global theme, unfortunately that did not resolve the issue for me. Unfortunately I cannot post a link, but it was posted by user u/scaryAstronaut in r/kde.