Have an odd situation with a Intel 125H based NUC with I226-LM+I226-V.
Typically 30s-60m post-boot with a light load, igc0/i226-LM stops
receiving packets while igc1/i226-V operates fine. igc0 can still send
but its rx-err/rx-crc counters tick up. After down/up link, the issue
reoccurs after another 30s-60m period.

Initially though it was one of the numerous i225/i226 issues, but
these are V4 chips with later V2.22 firmware. Disabling C-states >C1
(whether via the BIOS or hacking acpicpu_x86.c) avoids the issue at the
cost of high power consumption. Other purported i226 workarounds like
disabling ASPM had no effect.

The problem does not occur with basic Linux or FreeBSD test installs.

While experimenting, found that changing hw.perfpolicy from high to
auto and back to high fixed the issue. Feels like the BIOS or some 
other embedded power management firmware is triggering power savings
because it thinks OpenBSD cannot. Active frequency management via
MSR_PERF_CTL / hw.perfpolicy=auto (even for a short time) seems to 
disable the mystery power saver.

Modifying amd64/est.c/est_init() and amd64/cpu.c/cpu_hatch() to each
call est_setperf(perflevel=99) (setting an initial frequency for each
core as they come online) combined with kern/sched_bsd.c/setperf_auto()
firing (and refiring...) 200ms later also seems to do the trick.

Am certain there is a more precise explanation and would welcome any
thoughts. Thanks.