kern/56404: ACPI poweroff fails in current, works in -9

[nia%pkgsrc.org@localhost]

>Number:         56404
>Category:       kern
>Synopsis:       ACPI poweroff fails in current, works in -9
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Sep 15 21:00:00 +0000 2021
>Originator:     nia
>Release:        9.99.88 amd64
>Organization:
The NetBSD Foundation
>Environment:
9.99.88 amd64
>Description:
I have a machine that fails to poweroff in CURRENT, instead displaying these ACPI errors after devices are detached. This only occurs after several hours' uptime, and the machine is able to poweroff shortly after boot.

ACPI Error: Mutex [ACPI_MTX_Namespace] (0x1) is not acquired, cannot release (20210604/utmutex-367)
ACPI Error: Could not release AML Namespace mutex (20210604/exutils-151)
ACPI Error: Mutex [ACPI_MTX_Namespace] (0x1) is not acquired, cannot release (20210604/utmutex-367)
ACPI Error: Could not release AML Namespace mutex (20210604/exutils-151)
ACPI Error: Mutex [ACPI_MTX_Interpreter] (0x0) is not acquired, cannot release (20210604/utxmutex-367)
ACPI Error: Could not release AML Interpreter mutex (20210604/exutils-156)

Sometimes no errors are displayed and the machine simply hangs until it is powered off manually.

ACPI events (e.g. lid open and close) are still recognized and appear in dmesg.

acpidump output: http://procyon.is/acpidump.txt
>How-To-Repeat:
# /sbin/poweroff
>Fix: