Description:
Suddenly after systemd upgrade my server and laptop, which is LUKS encrypted and uses systemd-cryptsetup with keys in initramfs and root filesystem to auto-unlock, started to boot to emergency shell (photo of output will be attached). I started to investigate the problem, and find out that culprit was systemd-cryptsetup@root unit. Logs for that unit contained this error: "Failed to load key file "root.key": Argument list too long". After i extracted keys from initramfs file and chrooted to my broken systems, I decided to downgrade systemd to 247.4-2. After it was done and after initcpios was updated, both systems booted succesfully. This is the only change which was done and it helped, so the culprit is systemd 248-1. Seems to be, that FS#70264 is related and has the same culprit.

Steps to reproduce:
1. Setup system with LUKS full disk encryption which uses systemd-cryptsetup to auto-unlock partitions on boot with keyfiles in initcpios;
2. Make sure that you've replaced udev hook with systemd hook in mkinitcpio.conf, added sd-encrypt hook, and included /etc/cryptsetup-keys.d/root.key in FILES array;
3. Make sure, that you use systemd >= 248;
4. Try to boot.

P.S. Unfortunately I only captured output of server, which has "quiet" in kernel parameters. All other information was gained on laptop by removing "quiet" option, and by including /etc/shadow in initcpio's to get emergency shell access.