Not sure what to look for, the only relevant thing I see is:

Next step would be to run udevadm trigger while running udevadm monitor
in another session right after boot to see what events run and what
rules are executed.  That should help narrow this down.  Also compare
dmesg from boot with dmesg from udevadm trigger.

I'm not familiar enough with ubuntu to be much more help.

UDEV  [5341.078565] change   /devices/virtual/block/dm-1 (block)
UDEV  [5341.079255] change   /devices/virtual/block/dm-2 (block)
UDEV  [5341.082457] change   /devices/virtual/block/dm-0 (block)
UDEV  [5341.085049] change   /devices/virtual/block/dm-6 (block)
UDEV  [5341.087382] change   /devices/virtual/block/dm-8 (block)
UDEV  [5341.088389] change   /devices/virtual/block/dm-7 (block)
UDEV  [5341.089766] change   /devices/virtual/block/dm-5 (block)
UDEV  [5341.090079] change   /devices/virtual/block/dm-4 (block)
UDEV  [5341.090105] change   /devices/virtual/block/dm-3 (block)