ThinkPad X1 Extreme Gen 4 i8042 keyboard sporadically loses key-presses

Hi there,

I am using a Lenovo ThinkPad X1 Extreme Gen 4 (X1E4, 20Y5) that
sporadically loses key-press events, i.e. no key is detected when
pressing the key switch. Usually only single keys are missed, I have
not experienced multiple lost consecutive key-press events.

Lenovo has already swapped the keyboard, keyboard sub-card and
mainboard, so I would rule out a hardware defect with high certainty
(as only chassis, battery and screen are unchanged). The issue only
happens when using the internal keyboard, using an external USB
keyboard works flawlessly. I know two other users that experience the
same issue.

The X1E4 AFAIK accesses the keyboard via the i8042 driver.

An older ThinkPad model (the X1E2) had a firmware/EC bug [1] that
caused key-press events to be lost, so I can't completely rule out
that Lenovo messed up the firmware implementation again.

Affected systems: Lenovo ThinkPad X1 Extreme Gen 4 / P1 Gen 4 (Intel
Tiger Lake H). Mine has a Core i7-11850H.

uname -a
Linux vega 5.17.5-arch1-1 #1 SMP PREEMPT Wed, 27 Apr 2022 20:56:11
+0000 x86_64 GNU/Linux

Any ideas on how to troubleshoot this?

Thanks,
Thilo

[1] https://www.notebookcheck.net/ThinkPad-X1-Extreme-Gen-2-Lenovo-fixes-the-keystrokes-bug.464923.0.html