I updated to today's rawhide and then reboot's didn't complete until after
I removed /etc/udev/rules.d/70-mdadm-assemble.rules .
That's odd because udev wasn't updated today, though mdadm was. But
the above rules are part of the udev package.
I got warning messages doing the udev parts of the boot process that 3 of
the arrays were already running.
The device names for the arrays were different than they had been before
removing the rules file. So maybe the problem was that things were getting
done twice and removing either file would have worked.