How about a hard power switch? + crash report

[manawyrm]

That could be the sysrq-Issue. 

Try running:

Code:

zcat /proc/config.gz | fgrep SYSRQ

and check whether CONFIG_MAGIC_SYSRQ is enabled. 

As far as I'm aware that's a hardware issue in the audio/uart circuitry. 

Disabling SYSRQ via 

Code:

echo "0" >/proc/sys/kernel/sysrq

should fix the issue. (until a reboot)

Manjaro have disabled SYSRQs in our kernel for this reason.

I had the system freeze so hard that I had to take the back cover off & push the reset switch to get it to reboot.

You don't need to do that. Just hold the power button for 10 seconds.