mkinitcpio failing on Btrfs

I'm trying to install Arch on Btrfs but every time mkinitcpio runs it fails as shown in the attached screenshot. I've tried on the actual laptop which I'm trying to set up, and also on a couple of Hyper-V VMs set up as I usually do and I've never had this issue before. This happens when its run automatically after installing linux via pacstrap, and if I run it again while chrooted into the new system. If I format as ext4 instead I don't have any problems.

I have a single subvolume called root mounted at / and a fat32 volume mounted at /boot, and I'm using the latest arch install iso (2024.03.29). Any idea why this is happening? The Btrfs volume is on a single device so as far as I'm aware I don't need to add the btrfs module to mkinitcpio.conf