mkinitramfs uses /etc/fstab to determine the filesystem type in order to include the correct fsck in the initramfs. Something is wrong with your fstab, perhaps.
This email exchange
https://www.debian-fr.org/t/message-...oring/78032/23 (in French, sorry) is about an fstab with UTF-8 encoding, because it was created with an Office editor.
You could post /etc/fstab and a hex dump of it, e.g.
od -x /etc/fstab.
