Lattepanda Sigma freezes - limiting max C-state helps

My Sigma (32GB) runs 24/7 as a server with light to no load. OS: Manjaro with Kernel 6.6.40 and latest microcode.

On BIOS defaults (ECC enabled) it freezes every few days and only a power-cycle helps.

Disabled C-states --> runs fine for weeks. This topic helped me try that: https://www.lattepanda.com/forum/topic/334618

Enabled C-states plus limited in BIOS (Chipset - System Agent (SA) Configuration - TCSS setup menu - Tc C-State Limit) --> still crashes.

I tried all levels from 1 to 9 (none worked). It seems the OS overrides this setting or it generally has no effect.

Setting kernel-parameters actually limits the max. c-state:

intel_idle.max_cstate=1 processor.max_cstate=1

(edited GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub)

This workaround makes the Sigma finally stable, but supposedly consumes way more energy in idle.

There seems to be a BIOS bug(?). Can we look forward to an update?

Best regards