Booting from FAT seems to be broken in 8.00
Following to this guide - https://wiki.archlinux.org/index.php/systemd-boot#Grml_on_ESP installing SystemRescue on FAT partition worked fine till 8.00.
The errors that appears while mounting FAT partition:
FAT-fs (sdb1): IO charset ascii not found mount: /mnt: wrong fs type, bad option, bad superblock on /dev/sdxx, missing codepage or helper program, or other error.