Those conversion errors may mean it requires glibc-gconv.
Hi curaga
Both machine have mylocale.tcz onboot (depends on glibc_gconv.tcz)
They have the same version, too.
CorePure64
tc@box:~$ mkdosfs --help 2> /dev/null
mkfs.fat 4.2 (2021-01-31)
PiCore-aarch64
tc@pi3:~$ mkdosfs --help 2> /dev/null
mkfs.fat 4.2 (2021-01-31)
Anyway, there are 2 problems.
First, dosfstools.tcz is messing around.
(a corrupted partition can't get Syslinux running at all, returns to "BIOS menu")
Second, the kernel 13 simply can not boot with Syslinux UEFI, but kernel 12 can.