Stability issues. I get crashes compiling ZFS when clock is > 408mhz

I'm working on a new distro which is an ARM port of slackware64-15.0 beta.  The cooked image is here: http://mirrors.aptalaska.net/slackware/slarm64/images/helios64/

This image is built using the build scripts at https://gitlab.com/sndwvs/images_build_kit/-/tree/arm/ 

The high level view is that it's downloading the kernel from git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git (linux-5.12.y) then applying the patches found at https://gitlab.com/sndwvs/images_build_kit/-/tree/arm/patch/kernel/rk3399-next then builds the kernel with config https://gitlab.com/sndwvs/images_build_kit/-/blob/arm/config/kernel/linux-rk3399-next.config 

This is very similar to armbian, and the system seems to work just fine at first, but I cannot build ZFS without segfaults or other crashes.  I figured it was overheating or something so I added

echo 255 > /sys/class/hwmon/hwmon3/pwm1

echo 255 > /sys/class/hwmon/hwmon4/pwm1

which turns the fans on full.  The system gets very loud and nowhere near the 100C critical threshold, but when one of the fast cores (4-5) runs at 100% for more than a minute the compiler crashes (no reboots).

I started lowering the cpu frequency lower and lower until I could get through a build and the fastest I can set the CPU and be stable is 408mhz:

cpufreq-set --cpu 0 --freq 408000
cpufreq-set --cpu 4 --freq 408000

I also tried changing the voltage regulator per another post I found:

regulator dev vdd_log
regulator value 930000
regulator dev vdd_center
regulator value 950000

But that didn't help. 

Any other ideas on how to make this box stable at more than 408mhz?  It would be great to have slackware on it and be able to do things with it.

Thanks,

Matt