Arch Linux

[dhcpcd] 9.0.2-1 breaks boot

Description:
Some days ago I updated 10-20 packages and the boot was broken. These messages were visible in the console:

------------
[FAILED] Failed to start Load/Save RF Kill Switch Status.
[FAILED] Failed to start Load/Save RF Kill Switch Status.
[FAILED] Failed to start Load/Save RF Kill Switch Status.
[FAILED] Failed to start Bluetooth service.
[FAILED] Failed to start Load/Save RF Kill Switch Status.
[FAILED] Failed to start Load/Save RF Kill Switch Status.
[FAILED] Failed to start Load/Save RF Kill Switch Status.
[FAILED] Failed to mount /mnt/nas/backup-linux
[DEPEND] Dependency failed for Remote File Systems.
[FAILED] Failed to mount /mnt/nas/roby
[FAILED] Failed to start Docker Application Container Engine.
[FAILED] Failed to start CUPS Scheduler.
[FAILED] Failed to start Permit User Sessions.
[FAILED] Failed to start GNOME Display Manager.

After these messages the system didn't start the usual graphical login, neither the textual one.

Then I have downgraded all packages, using the archive mirror pointing to 2020/04/19 and it started booting again. Then i tried updating the packages one or two at a time and rebooting each time, and I narrowed it down to dhcpcd being the culprit of this failure.

But this time the behavior was slightly different: at the first reboot everything worked. I didn't install/upgrade any package, then when shutting down i saw some messages about failing unmounting home. The next reboot instead was broken, with the following messages, similar but a little different:

------------
[FAILED] Failed to start Hostname Service.
[FAILED] Failed to mount /mnt/nas/backup-linux
[DEPEND] Dependency failed for Remote File Systems.
[FAILED] Failed to mount /mnt/nas/roby
[FAILED] Failed to start Docker Application Container Engine.
[FAILED] Failed to start CUPS Scheduler.
[FAILED] Failed to start Permit User Sessions.
[FAILED] Failed to start GNOME Display Manager.

I tried another reboot and it failed the same way.

So in attachment you will find:
0: the first reboot after upgrading dhcpcd (not failing)
1: the first failing reboot after that
2: the second failing reboot
3: the normal reboot with the package downgraded (after chroot mounting from arch usb-key)

I wasn't able to connect to the support site of dhcpcd, the link from the github page doesn't work.

One thing i must say: in one of my many tries, maybe when downgrading or reinstalling or after chrooting, i saw a message from pacman reporting that the /var/lib/dhcpcd folder was permission 700 instead of 755, which make it unreadable from users. I did change it to 755 that one time, but i see that at reinstall it goes back to 700. That could very much be the root of the problem.

Maybe it's also worth saying that i don't have a wifi card on my computer.

$ pacman -Q linux systemd
linux 5.6.6.arch1-1
systemd 245.5-1

Please let me know if there is more useful information that I can provide.
For the moment I freezed the package version by putting it in the pacman.conf - IgnorePkg option, and upgraded all the remaining packages. the system now boot without problems so it's guaranteed that the boot problem comes from dhcpcd.