Sep 13 19:28:14 partman: WARNING: Not enough clusters for a 32 bit FAT!
...it appears to try and create the filesystem anyway, but, apparently it's in a state that the EFI firmware on the server can't understand when it comes time to try and boot the hard drive (just a guess)?
Logs from an unmodified 50format_efi.
Note the warning in the syslog:
Sep 13 19:28:14 partman: WARNING: Not enough clusters for a 32 bit FAT!
...it appears to try and create the filesystem anyway, but, apparently it's in a state that the EFI firmware on the server can't understand when it comes time to try and boot the hard drive (just a guess)?