Sporadic high CPU load after upgrade to 23.7.x

[karlson2k]

I upgraded my router to version 23.7.1_3 and after some migration fixes it has been working fine.
However, after two days uptime, I've found very high CPU load.
My typical load average is in range 0.18-0.35 for five and fifteen minutes averages. Even with full network load CPU load stays in these borders.
However, today the average load was 2.1-2.8 (for both five and fifteen minutes) with very light network load. I'm using passive cooled device and the temperature was unusually high.
I rebooted my router and for one hour the average load is below 0.4.

What should I check if I notice the high load again? Which command should I run to find the problematic daemon or process?

[newsense]

top and vmstat are already available, or if you're interested in visuals install htop from mimugmail repo