As the original reporter, I can add more information about this bug.
The dmraid package provides udev 97-dmraid.rules file.
This file has lines
ENV{DM_STATE}=="ACTIVE", ENV{DM_UUID}=="DMRAID-*", \
RUN+="/sbin/kpartx -a /dev/$kernel"
The used environment variable DM_STATE was set by
/usr/lib/udev/dmsetup_env (from multipath-tools package) and DM_UUID is
set by both dmsetup_env and 55-dm.rules (from dmsetup package).
However, Debian removed dmsetup_env starting from multipath-tools
version 0.8.8-1 [0] (dated Jan 2022) with the wrong comment that
additional variables are not used anywhere. [1]
As the result DM_STATE is not set anywhere and kpartx from
97-dmraid.rules is not executed any more.
The possible fixes are:
* restore dmsetup_env (the file could be reduced to set only DM_STATE
variable)
* replace the second rule in 97-dmraid.rules (see my patch in the
message above)
[0] -
https://metadata.ftp-master.debian.org/changelogs//main/m/multipath-tools/multipath-tools_0.9.4-3+deb12u1_changelog
[1] -
https://salsa.debian.org/linux-blocks-team/multipath-tools/-/commit/4ab9ce259ffa75ed3e2d145b3f2effc22af7b4c6
