I have a Raspberry Pi 4, and recently it has started to act very sluggish. During that time I found that the system load jumps up for a while. It isn’t processor use, but instead I/O use. After a while the issue goes away and the system is happy again.
I also had this issue 2 weeks ago. I found out my sd card was the issue. It had terrible write speeds suddenly, which caused hangups with system and logger, resulting in huge spikes. Created a snapshot, used a brand new sd card and all was smooth again.
The corrupt one had write speeds of 0.5-2MB/s speed suddenly.