I'm trying to track down repetitive hangs on an oldish laptop (10yo, 4Gb of mem, 2 cores, Kubuntu 18.04)
It now happens several times a day with moderate use (<10 tabs open in firefox, a bunch of other progs, nothing huge).

Sometimes I get a OOM but in most cases the user interface crawls to a halt for one to 30 minutes before things go back to normal. This is a recent occurrence (last 2 months). In most cases there's nothing in dmesg or syslog.

I've been trying to diagnose it without success, but one thing I've noticed with htop is that the load average jumps to 30 or more while the cumulative CPU usage stays below 10% and the memory usage (Mem+Swap) stays well below 4Gb.

1st question: how can the load average be so different from the CPU usage ?
2nd question: what else can I do? Can I run some stress programs and hope to get meaningful info?

[Edit]
Still waiting for the next crash, but I notice that swapiness is at 0. Shouldn't it be 60 by default ?