It looks like the accompany image.json for TEZI is also specifying /dev/mmcblk0. Changing it to /dev/mmcblk2 allows me to flash the device.
It looks like image_type_mender_tezi.bbclass::def rootfs_mender_tezi_emmc is hard-coding this to /dev/mmcblk0 Not sure if there’s a nice way to dynamically set this