Hello,
I also had the same problem yesterday. The process ksystemstats was using multiple GB of RAM.
Htop showed (I’m not allowed to include images):
/usr/lib/systemd/systemd --user
|- /usr/bin/ksystemstats
|- /usr/bin/ksysguardd
|- /usr/bin/ksystemstats (23.6GB memory usage)
I didn’t observe if RAM usage was continuously growing over time or just spiked at some point. I normally use hibernation and reboot the OS only after a couple of days. I have some of the stock system performance widgets on my desktop, but not sure if that is related to that.
I also noticed that sometimes the Plasma UI gets super slow and needs multiple seconds to start a simple program. After a restart it works fine again. But I’m not sure if that is related.
What would be the best way to debug this problem when it appears the next time? I coming from Ubuntu / Debian world and are quite new to Manjaro / Arch / Plasma. Therefore, I’m still lacking knowledge on how to debug the system in these situations :).