It seems as though the reliance on mounting the erofs and ext4 disks can happen somewhat arbitrarily in order as setting an explicit name for the ext4 disk in nix: base.nix ~line 311 seems to resolve the problem albeit it is reliant on their only being one ext4 disk hence I haven't opened a PR. There is probably a better solution for this.
boot.initrd.services.udev.rules = '' ENV{ID_FS_TYPE}=="ext4", SYMLINK+="disk/by-role/persist" '';
fileSystems."/persist".device = lib.mkForce "/dev/disk/by-role/persist";
My spindle runs asahi-linux fedora so arm I'm not sure if you will be able to reproduce this specific issue in your dev environment or not. Basically an CI workflow should trigger it involving microvm. I'm unsure if this is specific to my system in someway.