So I'm having this problem on three machines. I've also done the advice "udevadm hwdb --update" but the error still exists on the next boot.
Good thing about it, all is still working. My machines have a "hwdb.bin" file in "/etc/udev/hwdb.bin". I found a bug report on the arch linux bug report list as well as one on the systemd bug report list but no solution.
I will update this entry when I've found a solution or if the error disappears on one of the upcomming updates.
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